Having been through something similar, I would like to offer my opinion.
Leaving a marriage is utterly devastating, for everyone, especially the children involved. I left my DH, and it took me a few years to get the separation sorted. For the last 10 months of that, OM came on the scene. So, I was leaving my marriage regardless, but of course, now OM was around, I expected that when DH and I had separated, that he would be there for me. I had 2 children (aged 11 & 9) and OM had none. My relationship with OM was great. Plenty of dates, weekends away together, contstant texting and calling. About a week before moving out of the marital home, and into my new place, the OM dumped me. Coincidence? Nah, I don't think so. You see, having fun with a married woman, who can make no demands on you, is so much more fun, than actually having a proper relationship, and taking on a step-parental role to 2 kids. Now, I would have left my husband anyway, so it wasn't the end of the world, but imagine if I had left my husband for the OM!
Your Ex sounds like a dickhead, quite frankly :
A) He is messing around with a married woman (no decent bloke does that).
B) He didn't choose you, when you were a shiny 17 year old. He sure as eggs isn't going to pick you now, with all the baggage (2 kids and angry Ex, and a post baby body) that comes with. Sorry, I know that's very harsh!!
C) In NO WAY, does this man have your best interests at heart. He knows your marriage is rocky. He knows that divorce with kids is Horrendous, and yet, still, he toys with your emotions, and makes your situation harder to deal with. A good friend would step away, or give advice on how to try to save your marriage.
Your OM is lying about why he and his Ex separated. Men don't just stop wanting sex with thei wives for no reason. So, unless she gained 5 dress sizes, that is utter bullshit. So, I guess we can add a D to the points above : he's a liar.
He's already going cold on you. Why? I would bet my liver, that if you called him up this evening, and told him that you and the kids had left home, and you were on the way to his, that he would have his Nikes on, before you put the phone down. In fact, why don't you actually call his bluff and gauge his reaction –which will be to dump you--
The huge elephant in the room here, is the lack of sex with your DH. Guaranteed, if you and he had a fantastic sex life, you wouldn't be giving the Ex any headspace. So I think you REALLY need to get this back on track.
Finally, if you do ignore all of the above, ask your self these few questions:
-
Are you happy to see your children cry regularly, and to keep asking why you can't be a family any more?
-
Are you happy to spend alternate Christmasses alone (when EXH has the kids)
-
Are you happy to only spend half of the day with your children on their birthdays?
-
Are you happy to wave your children off on holiday with your ExH, and not worry about them going missing/drowning in the pool (because there's only one parent watching 2 kids)
-
Are you happy to lose half of all of your friends
-
Are you happy for ExH to hate you for the rest of time
-
Are you happy to have less money
-
Are you happy that the children will (in time) have a Step Mum, who might actually be a bitch to them (my ExH partner attacked my daughter, I had a thread on here at the time)
-
Are you happy for ExH family to never talk to you again
I could go on, and on, and on, about the painfulness of divorce. But seeing your children broken, is the worst of all.
TLDR : Ex is a red herring. Try, with herculean effort, to fix your marriage, before you throw a hand grenade in to your little family.
FWIW, I did go on to meet a lovely man, and am now happily married. Kids are grown and they get on well with him. BUT. If I had my time over, at the very least I would have waited until they left home, to leave the marriage.