Please, OP, re-read some of your earlier threads and try to imagine your reaction if they'd been written by someone else. Because they don't paint an encouraging picture, do they?
Almost before your brief encounter had got started (because, let's face it, he is not a partner in any understood meaning of the word) you were worried about how you would deal with his alleged BPD and how there had "already been some major issues regarding sexual impulsiveness and fear of loneliness that resulted in him sleeping with somebody else in the same weekend as myself". Now while I'm no expert on BPD, in the context of what was to come, he does seem to have set the stage to behave with complete disregard for fidelity on the grounds that his impulsiveness means he can't control the need to fuck someone else.
A month into this brief encounter (for he is not a partner in any understood meaning of the word) you were asking if it was reasonable for him to spend every Thursday night with this part-time lesbian. He excused the need for this arrangement by telling you she was "...as his best friend part of his support network regarding the mental health issues i mentioned".
Your next thread ponders the reasonability of him refusing to allow you to meet his friends. Yet again he has a wonderfully creative excuse for this bizarre state of affairs, namely "He says he acts different with them than he does to me and that has lead to bad experiences before.".
Now, two months down the line, he and the girl who is Mainly A Lesbian are planning to go on holiday together. You aren't invited because she isn't comfortable meeting you.
How much more humiliation are you prepared to take?