my son has left his wife

My MIL went through this exact situation with another of her sons. She had been close friends with her DIL and when her DIL found out about the other woman that was the end of a lovely friendship, which affected my MIL for the rest of her life. Your DIL deserves to know the truth and preferably from you, otherwise your GC may become estranged from you.

AC shouldn't bounce back to mum and dad when things go wrong.
I agree and I would not want to have him living there knowing that he has left his wife and children for another woman.
He's grownup enough to have married and have a family so he should be able to stand on his own two feet.

Don't be the one to tell your DIL but tell him he must do so. I hope you can remain friends with her and continue to be supportive to her and the children.

I think it is rather sad to say 'he has fallen out of love with his wife' as one poster did. It's not just about him when there are children involved - most marriages are not a total bed of roses - well, if they are, there are often some thorns which have to be negotiated too.

You must of course not say anything. It's up to them to come to terms with what is happening. Equally you need to maintain a good relationship with your DiL. A difficult line to tread, but all you can do is encourage him to be honest. This is very common and you will all get through this.

So much conflicting advice and of course it's all valid because we all have different points of view.

If this were me, I'd keep up the usual loving relationship with DIL and children.
If there is, at some point, a divorce, you will already have a good grounding for continued contact with the grandchildren and their Mum.

You said this is uncharacteristic of you son and maybe that's what caused the split - he's not the man she married any more and they both needed space to re-evaluate the relationship.
You are hoping they might get back together and perhaps they will.... but maybe that's not what's best for them. Only they can tell.
Just keep being your loving, supportive self.

Agree with Telly that it is not the OP's responsibility to tell the DIL. It will only make matters worse.

Grannibobs - stay out of it and set a deadline for your son to move out. By saying anything you will appear to be interfering and taking sides and risk not seeing your GCs as a result.

If your DIL challenges you you could say that you did not expect the relationship to last so you didn't want to upset her needlessly.

It's not for you to tell your DiL but you do need to have a conversation with your son about the whole situation. Tell him you don't feel happy knowing about his new lady friend and his wife not (does the 'girlfriend' know he's married I wonder?) and you won't lie for him.

It's too simplistic to say he needs to find somewhere else to live - he probably can't afford too!

It’s time for your son to ‘man-up’ and tell your daughter-in-law that he is involved with another woman. It seems she still cares about his welfare but he doesn’t care about hers. You don’t say how long they’ve been separated, but it reads that it hasn’t been too long, I would have thought he could have done with a bit of breathing space rather than jump into another relationship. Personally, I wouldn’t be the one to tell your daughter in law, that is up to your son. Honestly, it seems so easy these days to walk out of a marriage because mum is there to pick up the pieces. That isn’t a criticism of you, it’s happened to me with one of my daughters.......and yes, I was there to pick up the pieces. No one wants to see their children struggling but it does make me wonder if separation is made too essy.

Grannibobs I don't quite get why you've allowed your son to come back to live with you. Surely you're aiding and abetting the break up of his marriage? You say you love your DiL and Grandchildren and I don't doubt this but why have you made it so easy for your son to abandon his family? By the way, you say he's "come home" but surely his "home" is with his wife and children. In my opinion, he needs to man-up, return and give his marriage it's best shot (if only for the sake of his children). It's so unfair to be putting you in this situation. If you can bring yourself to then I would give him an ultimatum in that if he wants to start over with someone else (possibly commiting adultery) then you're not going to be party to helping him. Sorry if this sounds harsh but I'm guessing he knew exactly what he wanted when he moved back with you.

I wouldn't say anything or tell anyone!! Mention another woman and you will ruin whatever chances are left to save your son's marriage.

You can be supportive but be discreet. As long as he's staying with 'mom and dad', the possibility of a serious relationship is less likely. Letting your son stay with you so he has a quiet place to think things through and get his priorities sorted, may actually bring him to his senses and (hopefully) save his marriage.

Afterthought: Perhaps you could suggest that your son and DIL go to couples counseling.

Marriages break up and one of the most difficult things to sort out is the economic aspects of the break up. The son moving back to his parents seems to be one of the most common ways to do this. That said your son is going to have to sort out things between him, your DIL and his new partner. Relate as well as doing counselling for trying to save relationships also offer separation counselling. Perhaps your DS and his wife would benefit from this. Finally this is only the start of a long process. Couples with children who decide to divorce have to go to mediation to sort things out and it can take 6 months. The important thing for you is to stay friendly and supportive for both parties. If your son does tell his wife about the new woman you should make sure she knows how troubled you have been about the same thing. It is possible in the future that you will have to build a relationship with this new woman, but make sure your DIL always knows she has a special place in your family.

I don’t agree with posters that say your son shouldn’t come home, of course children however old should always have a bolt hole of ‘home’ I think of my house as still theirs if they need a home
Stay friendly with the daughter in law and support her as much as possible, without talking about your son Tell your son to keep his life outside his marriage completely to himself that you don’t want to hear, meet or know anything about any new relationships
Marriages break up for many reasons and every poster on here will be guessing according to their own experiences or those of friends relatives and all may be wrong
It will all sort out in the end it always does, this will just be a nasty dream soon

I really think it's unlikely they'll get back together as he left and is already in another relationship - no matter when it started. Apparently most men do not like feeling ashamed, and will do almost anything to avoid it, so he is unlikely to do the honest thing and tell her voluntarily face-to-face. However, it would be awful for her if she found out from someone else so giving him a deadline to tell her seems a good idea. Otherwise his suggestion of living elsewhere might be the best solution.

I was discussing this type of scenario yesterday with my friends over coffee.
Out of 5 of us (all grandparents), 3 have experienced family break-ups and all 3 have said there are still ongoing problems.
One has no contact at all with the DIL and grandchildren as DIL moved abroad back to her mum’s and refuses all attempts at contact. Adult DS hasn’t seen his children for several years now.
Grandparents often lose out when adult children split up so I think you need to focus on supporting your DIL and the grandchildren as much as possible. Hopefully, when the dust settles, DIL will still allow you contact.

I wanted to send you a private message on this but I am unable and the message I am getting is that you are not 'set up' to receive pm's on this subject.