Hi Makita: The one friend is currently not really speaking to me because I rejected his sexual advances.
Probably a good decision to not spontaneously get into a sexual relationship with him. BPD can make things complicated. It is definitely wise to think over the situations
My other friend I'm supposed to be moving in with... but now they've totally shut it down. I'm supposed to be taking on a part care role for them as there is currently one person doing it and they feel ridiculously overburdened and don't know how to step back a bit without it seeming like a complete and utter rejection. To be honest I'm incredibly confused
Perhaps it is good for you that the move is shut down. What exactly would a "part care role" be? Would you be moving into someone's home, where you get free rent? Who would determine if you would get kicked out (the person with BPD)?  :)oes the person self harm or have suicidal ideations?
The fact that the other person is overburdened should be somewhat telling. If this is something you might take on in the future, it would be wise to learn as much as you can about setting boundaries and communicating with people with BPD (pwBPD).
There are a series of lessons at the link below. It can help you to be prepared. If not for the situation with sharing a home, then for possibly continuing a friendship.
LESSONS