I mean, I understand why he got dragged, but it wasn’t because he’s a psycho. He obviously loves you OP, and that made him make two horrible decisions:

1. He stayed the relationship when you asked for an open emotional and physical relationship with one specific person who was and still is (assuming Christina is the “friend” who pointed you to his post) a threat to your relationship with him.

2. Doing something spiteful to you because he was hurt that you chose someone else.

But you made an equally horrible decision by not breaking up with him when you found out what he did. You too doubled down on a bad hand and decided to stay with him, and now you two have a child on the way.

My advice is to get individual therapy, and ask him to get couples therapy, to be able to functionally coparent the kid at least, and secondarily to figure out if you two can salvage a healthy romantic relationship (he also has lingering issues about what you want).