my son has left his wife

I don't know what the reason for leaving was. My son and daughter in law both said they had been having problems for a while but didn't really go into detail. If I'd known he was going to go off with someone else I wouldn't have made him feel welcome in my home.

An important issue for you must be seeing the grandchildren. If you fall foul of your DIL by keeping this secret then you may put this in jeopardy.

However, I am not suggesting that you tell her, simply that you continue to be clear with your son that you are not going to collude with him in this - and that he must tell her what is going on. She is likely to be understandably furious when she finds out and knew that you were aware all along.

I agree with what you say. I've told him in no uncertain terms how wrong he is. I don't want to know about this woman. I've told him numerous times to sort things out. My daughter in law doesn't deserve this.

" The DiL will now think that you condone this behaviour and are party to it."
Good point EllanV.
Grannibobs - if your son wants to leave his wife and family he needs to find a place of his own to live. Is he working?
It's a very sad situation, but it's their problem, not yours.
I have a close friend who is going through the same thing with her son, though he doesn't live with her. She's so upset, it has changed her.

You don't say what was the original reason. or explanation for the split. As a completely detached person. it seems to me that there is a strong possibility that this 'other woman' was already in the picture before the split and that your DIL may know this but is choosing to turn a blind eye in hopes that it will fizzle out and your son will return to his family.

Thank you all for your advice. Initially my daughter in law asked me to let my son come to my home. She was very worried about him and wanted me to be there for him. He had had mental issues in the past and she was worried because of his behaviour. It is totally out of character for him to behave like this. I told my son since learning about this other woman that I'm really not happy so he said he would leave. I told him the real problem is that he isn't being honest with his wife and if he doesn't tell her I will. He's aware of this now but I still feel it might not be right. I'm torn.

Basically he is using you and not respecting you. He is an adult and needs to get on with it.

You must have quite a big house which is lucky.

I wouldn't have taken him in under those circumstances. It's so mean to put you under this obligation because he has another woman. The DiL will now think that you condone this behaviour and are party to it.

I'd have sent him right back to sort it all out between them.

I haven't been in this situation but I would keep quiet unless my DIL asked a direct question. I wouldn't lie. I would explain that to my son. I think you just have to give him time and see where that leads. Of course you are sad and I feel for you.

I agree with FarNorth.
Are the DC very young? Children notice things and if you don't tell their mum she'll find out soon enough.

I agree with Farnorth , it’s not your secret to tell and I suspect your DiL would shoot the messenger!

However, you are enabling your son , so I would have a conversation with him and tell him you’re not lying for him. Put the responsibility straight back on him .

For what it’s worth , if he were my son , I wouldn’t have made it so easy for him to leave his wife by offering a refuge. I know you love him but it’s so easy to move back home with Mum. If your escape had not been there , might he have stayed at home ? Worked a bit harder at his marriage? Not found it so easy to cheat?

I don’t know but I really feel for you in the situation you’re in .

In a similar situation I simply said that I wasn't happy with the situation, that I was not ready to meet the new 'friend' and that he/she would not be welcome in my home.
If you mean he has moved home to your home he has no right to impose this situation on you. Is he bringing her to your home?
Your house your rules.
Rightly or warongly, I'd be tempted to say how unhappy yon are about feeling disloyal to your DiL and that if he doesn't discuss things with her then you will.

If he doesn't want you to be involved in what he does, and what he says to his wife, he shouldn't be living in your home.
Maybe a suggestion that he find somewhere else to live could focus his mind on being straight with everyone.

I think your son has to be honest with his wife.
Tell him you can't stand lying to her and that you feel you will have to tell her if he won't do it.
If he doesn't think their marriage is over, why is he seeing someone else?