I understand how you still love him and know how painful that is, but he does have a child now so if I was you, I would not pursue your XH. I would not have accepted an R with my XH if he had got either of his OW pregnant, even though we have 4 daughters together.
I'll tell you from experience, my MIL hated me (and my own mother) and spent the majority of my M, trying to start fights between me and H.
How do you know your MIL isn't just gossiping? You can't know what his new partner is like without seeing for yourself. If MIL doesn't like her, if she wanted you to reconcile, it seems reasonable that she would say bad things about him.
And it isn't fair to split up the family of a baby on the basis of a pre-concieved judgement about how his/her mother behaves.
I'm not bashing you either (just pointing out my honest opinion and what I would do), and if that was me, I would seek C about my unresolved feelings, I would concentrate strongly on my current R and I would find a way to have closure with XH.
I hope this advice doesn't upset you, that isn't the aim, but your current bf sounds as if he's sticking by you, your XH has a family now so if you were to rush in and break them up, it would be causing upheaval for 3 families (yours, XH's new family and bf and his family).
This BB is an excellent place for exploring painful feelings, and GAL work, though, so please keep posting. I'm sure we can help you on your journey.
