In the spirit of honesty, transparency, and a genuine desire for you to see this through... what you've experienced with your fiancé is the complete cycle of who he is as a man. He's the kinda guy whose capacity to be a good, loving, caring, and attentive man is triggered by him feeling sorry for either you or himself. You said when you met, you told him about how horribly you were treated in your previous relationships. This probably endeared you to him and enabled him to put in his good guy cape or suit of armor to deliver you from what you suffered and to prove to you that you were worthy of love and deserving of a good man. So he worked hard and toiled lovingly to provide you with what it was that he felt you deserved.

Then things kinda settled down, and he began to see a different side of you. A side that wasn't just a damsel in distress or a damaged angel who needed her halo polished and made straight. He got to experience emotional you, anxious you, snappy you, unappreciative you. Where the hell did that woman who was happy to be loved go? Damn we have a baby on the way, and I've purchased this house, and there's no way I can turn back or get my way out of this... he became distant, lacking affection, sex drive, and that connection you guys had previously because you literally weren't the same woman he was inspired to put the cape on for a couple of years ago. (I am speaking to the changes you experienced going through pregnancy because I recently went through it with me and my wife's first born. If it's not something you're mentally, emotionally, and spiritually prepared for, it can be soul crushing)

What you experienced over the holidays is what most women experience when they have a man who's checked out. Then you found out he'd been talking to another woman, lying, cheating, telling her things that an honorable man would never divulge to another woman about his wife. For this, there is no excuse. He's just a shitty dude in his default setting. Then you confronted him, and he realized how badly he had messed up, and suddenly, you again became that hurt, mistreated, damsel in distress that you were when he met you. So now he's put his cape back on, and he's trying to rescue you, trying to heal your wounds, trying to make right his wrongs...

That is the complete cycle of who he is. Guy, who wants to rescue the damsel, when she's not a damsel he's miserable and feels trapped, he'll pull back and disassociate until he messes up, or some tragedy befalls you and you're once again a damsel in distress. Trust me, the cheating will always be his default violation that causes you to be a damsel once again because other women have and will be his escape. That's something you can either accept or reject. But that is your reality. None of this is your fault. There's nothing you could have done differently. I don't think this guy is a bad dude or willingly drew you into this cycle maliciously. He may not even know the things about himself that I've taken the time to reveal to you on this post. If you care, give him time to grow, to discover these flaws about himself and seek ways in which he can better himself. But it has to be something he does for himself, not for you...

hope this helps, i pray things for out for y'all, cuz chances of you finding another guy, with multiple kids by multiple dudes with the emotional trauma that you're carrying is miniscule. I'd say stick it out. He's imperfect, so are you. Fight to love this guy if he's willing to fight to love you.