"I'm ready to find a great guy who will help me raise S!"
How does that sound?
Excellent!
In my own experience, talking about YOU finding someone new ALWAYS gives them pause.
I think that's the biggest reason my WH is still living in the house.
After I exposed EA in March, he told me he was leaving, he'd had enough, and he wouldn't be "at all" jealous if I found someone new. I said that was good, because I had every intention of replacing him ASAP.
BTW - I hoped he still felt the same way in about 15 years when the girls' "new dad" walked them down the aisle, because he wouldn't be invited. I would NOT repeat the drama of our wedding*, I'd just do what Mrs. X did**.
I said it in a fit of anger, but I believe it made him think twice.
Ah, Catholic guilt. So useful sometimes!
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*His parents were separated, both brought a lover to our wedding, all four stood side-by-side in the front row of the groom's side staring daggers at each other as my entire family watched, completely aghast. It was a hell of an introduction to his dysfunctional family, and he was embarrassed by it for years.
**My grade school BFF's dad left her mom when we were 19. At the final divorce hearing, Mr. X showed up with a new 30-something girlfriend -- who was 6 months pregnant with his child! Mrs. X (who was in her early 60's) was SO devastated, she stayed in bed for a month afterward. My BFF was SO disgusted that when she married later that year, she didn't tell her father (with whom she had once been very close). Mrs. X decided to rub it in by putting together a beautiful wedding album, which she had delivered to Mr. X's office. He apparently went into a crying jag when he saw it, got drunk and stayed drunk for two weeks - because, SURPRISE, SURPRISE - he was already having challenges with the girlfriend and new baby and missed BFF terribly. That she'd gotten married without telling him FINALLY made him realize just how much he'd damaged their relationship. That was in 1984. It has never recovered.