I don't know what to do

welbeck

seems like you have unwittingly been subsidising his other household.

This^

OP, please , please visit a solicitor and get proof of the 100K you gave your daughter so if/when she divorces him, he cannot claim half of everything. You gave it to them both, but he has not any claim now because he is cheating.

Another thing I would do is get an investigator to get photos of him with the other woman to back this up, so you have proof if you ever need it. I would not rush to tell your daughter, but if the muck hits the fan, you need to protect her by making sure he doesn't get 50% of everything. The dirty, cheating B@astard! I would actually get your ducks in a row before considering whether to tell her.

I'm so sorry but it seems like he's using you both

Tell your daughter. The longer you leave it the worse it will be. Whether she knows already or not is irrelevant. Been there. Kept a secret. Didn’t end well.

You need to disabuse yourself of the notion that your son-in-law is a wonderful, husband, father and son-in-law. He is not. He is duplicitous, unscrupulous and greedy, enjoying a double life to which you are contributing, whilst neglecting his wife and children.
He must possess great charm as you say you love him so much, even when you have discovered how he is betraying your daughter.
If you expose him it may well be the catalyst that prompts him to finally move in with his mistress; she is not going to give up, having hung in there for ten years, and you may discover that she is involved financially in the business. Your daughter may well be aware, and is likewise trying to sit it out.
The most worrying aspect is that he works for himself; their house may be security for his business and in the event of a break-up half is legally his. Certainly check out his business details and his relationship with this woman.

I don’t see any way for you to keep this from your daughter. She may have suspicions, she may know. It’s also possible she’s been gaslight and manipulated for so long she believes his lies.
Imagine finding out your parents knew your husband was living part time with two families but didn’t talk about that with you.
I’d be more concerned about the emotional fall out than attempting to secure the £100,000. Ignore the advice to somehow get the money secured. You gave it to them. It theirs and will be part of any financial settlement if divorce follows.
I know we are still in lockdown but - in your shoes I’d be arranging to sit down with my daughter, without the children and find a way to talk this through.
One of my friends discovered his father had run two households - father was in his 80’s, my friend 50 years old. The other family had three half siblings. It was a shock to all of them.

I agree with eazybee your son in law is not a nice man if this is definitely true. You need to stop any financial support Gingerbeer and try to find out how their finances are being managed. I am not normally an advocate of interfering in the lives of adult children but in this case I think you need to raise concerns with your daughter.

He’ll probably be relieved. It must be damn hard work lying to everyone. And don’t forget he, and even your daughter if she knows, has been lying to you for a long time. Draw the line. Open the box. Deal with the fallout.

Have you done a check on Facebook, etc. to see if the other woman has an account? If she has you will see if she presents herself as married/single/in a relationship.

Secure finances and secure the £100K you gave them, was it a gift or a loan? Make sure everything is watertight financially before tackling your SIL and talking with your daughter. Whatever happens it has to be your daughters decision with your support. I think I would have to drive by the other house on a few occasions to arm myself with as much info as possible. He doesn’t deserve your daughter and obviously wants the best of both worlds, he can’t!

Personally, I do not think you should tell your daughter.

You risk her not believing you and whether she does or not, she will be hurt.

Unless your daughter is quite incredibly naive, the fact that her husband cancelled holidays with her on account of "work" should have rung alarm bells, as she knows he has had one affair.

If you start your own business it is quite normal "not to have any money" for a few years, so how long is it since he started that business and take recession and covid 19 into account please.

I think you should do and say nothing. Do you honestly want to tell your daughter that you have been checking up on her husband behind her back?

If you must say something, talk to your son-in-law and mention casually that someone with exactly the same name as him is living at such-and-such an address and is he a relation?

Or be honest and ask him straight out if he is carrying on with another woman behind your daughter's back, because if so, either he tells your daughter what is going on before the end of the week or you will.

I would express your concerns to your DD. I see no other way forward. If she doesnt know and later finds out you did know she would understandably be very cross with you. If you do choose to tell her please let us know how it goes. Very difficult situation. I would advise no more checking but just share your concerns. Good luck

If your son lives in the same council area and has an unusual name there will be other people who know about his situation, and may regard your daughter as the interloper.

This is a serious situation and you need to handle it very tactfully. How do you think your daughter will respond if you tell her you have been running checks on her husband? I don't blame you at all, but bearers of bad news get blamed,
and if she knows at least part of it, and most wives do, she may be unhappy about you exposing it and forcing her to take action.

Your dd could also be ok with this arrangement, that is also a possibility

It's their business, not yours. If I were you, I'd keep my mouth firmly shut!

The chances are that your daughter knows all about it, tolerates the situation - and doesn't want any discussion about it.

@Gingerbeer I've read through this, and firstly, for you. I'm SO pleased your husband is with you, you must obviously be distraught to have discovered this.
Because of the Electoral Roll angle, it does seem that he has two settled homes and has for years, plus of course the fact that you've seen him and the other woman together coming out of the house.
To me, there are 3 options:
1) to say/do nothing
2)to tell your daughter what you've discovered
3)for you and/or your husband to confront the b., tell him what you know and ask him how he intends the rest of his life to play out.

Could be that your daughter, as Hetty wrote, knows about the situation, but I'd want clarification from him of this.

I'd certainly want to shield your daughter from unnecessary pain.

Again, all the best to you, I'm so sorry.

PS Years ago I went to the funeral of a man I knew through my work. And that was when his second family came to light. Two grieving widows, children from one of them...

I'd forgotten about this until just now.

You daughter knows what’s going on for sure the pattern is too obvious, she chooses to gloss over his lies, wether for love or security doesn’t matter. Maybe she is biding her time, from what you say money is tight, so if they split up she would loose the house and all the disruption that would cause.

She is keen to hang onto what she has got so I don’t think I would say anything. Dont help him financially, in fact keep the cash in your own control so you can help out if the marriage does end.

I think this is one of those situations where you are damned if you do and damned if you don't.

I don't what I would advise but I think a lot depends on your daughter's personality and relationship with you. Is she likely to believe you or him? It seems he has form for this sort of behaviour so, in theory, she ought to believe you.

Would your husband be willing to be with you if you mention the situation to her? This might add weight to your argument. Not sure if that's quite the right expression.

I’ve read all your replies and thank you for them. I’m still in turmoil. I don’t think there is one opinion or piece of advice expressed here that hasn’t already gone through my mind. The other woman doesn’t go under his name and I don’t think there are children. She certainly knows he is married as my daughter received nasty messages claiming ‘he’s mine’ when she was pregnant. There were rumours at that time that she was his other woman. Also, he worked with her before starting his own business. It’s only looking back now that I realise there were danger signs. He seemed so loving and caring and still does when he’s around. I love him like my own. He’s been in our lives since childhood. They were inseparable from the age of 11, childhood sweethearts, engaged then married.

What worries me is if others know and are gossiping behind my daughter’s back. I think I would feel betrayed and humiliated if someone close to me knew and didn’t tell me. Then there’s the risk she knows already. I have no wish to interfere or meddle. We are a close caring family but we all lead our own lives. I’d hate for any of our children to feel betrayed. It’s a poor shame if your mum can’t look out for you.

Someone mentioned making sure the property ownership was secured for my daughter. That is a subject which I will raise with her. The house is now reaching completion and they are living there so it won’t seem odd to mention sorting out the legal bits. I would add that we gave them the money as a gift with no strings attached so that our grandchildren had a decent roof over their heads. By the way, they lived with us for a year as their house had no roof.

Thanks again for all your responses. It has helped no end just being able to share it, as at the moment I don’t feel able to talk to anyone about it.

How about getting a private investigator to get to the bottom of it and get proof, which could be delivered to your daughter anonymously.

This would help her get a significant advantage financially if she decides to divorce him- you could just be there when she needs you, then.