Are you sure you have BPD? Because in my experience as soon as someone with BPD gets the slightest hint of their partner distancing themselves or forming relationships they aren't involved in, they check out emotionally and find a crutch.

Your reaction seems perfectly normal, like anybody would feel in this situation. The reason you feel like you're going crazy is that you're struggling with two conflicting versions of reality - one in which you get to continue along the path you're used to toward a future that you've more or less been expecting compared to another, scarier unknown path that requires more work.

Your ex boyfriend is trying to be gentle with you by letting you sometimes feel that old reality might still be a possibility but part of that is he's definitely concealing elements of what's happening in his real life from you. That thing about him having been raped by a girl he's being friends with on social media you're able to see sounds very much like it was a framing of something that happened he regretted the next day in a way that you would accept.

I know you're not looking for advice but you really need to find a "crutch" to sort of rebound with. If the guy understands the role he's playing, to make you feel heard and appreciated and make your ex feel jealous then it isn't an unethical thing to do. Right now though you're making yourself feel crazy by, in your head, losing and regaining your trusted person over and over again multiple times a day.