I’m sure I don’t have the whole story. This is so complicated. But my first impression on reading your letter was asking myself why you stayed with in a “rough” relationship with a guy who was constantly accusing you of cheating. Now he says he’s “totally single.” But he’s not. As you pointed out, he’s tied to a child for the rest of his life. The fact that he is uninvolved with the woman is, to me, a negative comment on his character. He does have a responsibility to her and his child. You deserve better — much better.
I do understand your pain. Dealing with infertility is one heartache after another. It’s possible you are mourning the baby you thought you would have with him more than the guy himself. I do understand your longing and grief. I also understand your disappointment and anger. But I don’t think the way to resolve this is to return to a guy like him.
I urge you to find a therapist immediately. You need more help and support than I can give you in an advice column. A therapist can hear the details and can help you come to some new understanding of just why someone who treats you so badly is the only guy “who sparked your soul.” You need support in grieving for the relationship and for the failed attempts to have a baby. And you need some guidance and support in finding the kind of guy you (and any child you have in the future) deserves.
You are still young. You have time to do your therapeutic work and to find the right man to love and with whom to have a family.
I wish you well.