Sorry you're going through this emotional stress.
Re (from Post #1
"I still have very strong feelings for him, and he for me. I would like to be able to still salvage some form of relationship with him, even though I understand that it will be drastically different than it is now.
Is this foolish of me? Has anyone successfully transitioned a relationship like this? Or should I just be cutting my losses before we can't stand the sight of each other?"
What you're describing is a transition from a triad (or ex-triad) to a V, with considerable emotional distance, perhaps, between you and your girlfriend (or ex-girlfriend). You're also proposing to continue that (V) relationship without living with them.
On paper, there's no reason why such a thing would be impossible or unthinkable. I'm sure such transitions have been done before, with success. But now would be the time to present this proposal to both him and her. Both of them would have to agree to the idea before it could become an ethical reality. She in particular would have to agree to it. So I'd try to schedule a sit-down with them soon so the three of you can talk it over.
If your ex-girlfriend says no to the idea, then you'll probably have to leave it at that, unless your boyfriend wants to divorce her. But all three of you should be extremely reluctant to go down that road, especially when there's a child in the equation.
Probably the sooner you can talk to them about it the better, if for no other reason so that you know what to expect, and can start emotionally preparing yourself. Don't put all your eggs in that basket, but don't necessarily throw the basket away either, not until you've heard from your boyfriend and ex-girlfriend whether they're both willing to try it.
Good luck and I hope the advice here will help.