Nick.....
You are either a patient man or, you are a marshmello. If it was me......I'd be gone. I'd pay child support for my son, get visitation rights and be done with her. Yes, it is hard to leave someone that you love, but no way would I let her walk all over me. Ain't that much love in the world. I would find a way to get over her and heal my broken heart. I wouldn't get involved with her again, even if she did get help. I can put up with a lot.....being friends with other guys and even going out for lunch or something but, if ya hop in bed with him, you made your choice......I'm outta there.

Good luck to you,