how do I just break up with him (again)?

By telling him that this relationship isn't working for you and that you're better of going separated ways. Then you go no contact for a while and just talk to him through a lawyer.

His Mom [44] adores me and always asks me to hang out with her on weekends. He kept the break up a secret from his fam and I literally had to stay with him through out the whole break up.

WTH? It's not like your bf is keeping you hostage. If you break up and he doesn't tell them, you can mention it to his mum next time she wants to hang out "hey, I'm not sure if you know, your son and I have broken up since it didn't work out anymore. I just wanted to let you know in case this changes your opinion about wanting to hang out with me".

Just please don't let her or anyone else talk you into getting back together and giving it another try. If they do, just be honest with them "bf/ex cheated on me, behaved shady and didn't show any interest in the pregnancy."

I'm way too deep into this already delusional,yeah..maybe.

It's not too deep yet. You're not living together and you still have time to figure out custody arrangements with a lawyer.