Welcome MBM!
You are in the right place talk with people with similar experiences. Have been able to find some time to read any of the lessons and basic tools? You can find them on the right hand side as well as in the upper drop down menu.
I want you to know you are not alone, or the only person dealing with things like this. I can identify with the frustration of a SO trying to force their own thoughts on you as if they are your own. The classic You are thinking X! No I'm not. Yes you are. exchange. It can really put you off balance. I could get confused for a moment when my wife would say "Well just divorce me like you want to! I know you want to!" When the word divorce or breakup has never left my lips in our 10 years together (maybe it should have ). If I tried to work through or talk about something difficult (real life stuff... .finances... school choices for the kid... her quitting her job without warning... .etc... )... .it meant I wanted a divorce. Ugh.
I would urge you to be cautious here, as pwBPD can really project their things onto you. He cheated... .and he probably has thought about divorce and taking your kid from you, to punish you for making him cheat (nonsense). Now keep in mind I am just guessing here. He is prepping other people for what he imagines you will tell them when the "inevitable in his mind" divorce happens. Try not to engage or even defend yourself to those people. It won't go well. You are better off letting your actions speak for themselves.
And remember: What can you do to support him? Take care of yourself and show him how a healthy person faces the world. Let him work through his stuff, or not. His choice.
You said recently you found out he had BPD? How did that happen?
If he is diagnosed, is he in any sort of treatment or therapy right now? Or has he ever been?
Most importantly... what about you? What are you doing to take care of yourself?
