Well I have a couple suggestions for you; I'm sure that others here will have more.
1. Stop talking about BPD, and read about it when she isn't looking over your shoulder. For that matter, if you have books about it, put them someplace out of sight. And absolutely, don't let her see any of what you are doing here!
Whether she has BPD or not, labeling it and talking about it isn't going to help either of you much if at all. Specific behaviors are driving you to the edge. Here we will help you use tools to reduce those behaviors or at least reduce your exposure to them.
What matters is what happens when you start using the tools.
If she brings up BPD you will need to respond, but hopefully not often.
2. She has issues around sex. How are you handling it? Not the fights about it, but amount/quality of sex? If this isn't a huge and immediate problem for you, then let it slide for now, addressing the conflict directly instead.
3. Raging:
Then, just like someone had flipped a switch, she started ranting on about how I can’t force her to have sex with me or love me.
... .she is upset with me because I seem to be in a mood with her!
You can address this very effectively with boundaries. We've got a couple workshop devoted to them here:
BOUNDARIES: Upholding our values and independenceBOUNDARIES: Case studies I highly recommend reading them both, however here's the one I'd suggest you use:
Boundary: I will not be verbally abused [You can define where this crosses the line]
Response: If she starts verbally abusing you (raging; putting you down; etc.), remove yourself from her.
Options: Go into a different room. Take a walk around the block. Go to a coffee shop or library or friend's house for a couple hours.
If she tries to block you from leaving, don't let her do it. Physically forcing past her is dangerous; a better option is telling her that you will call the police if she continues to block your way out.
A couple refining tips on how to go away: Avoid telling her that she is unreasonable or you are going away until she calms down. This is true, but not helpful. A better thing to say is that you are going away so you can calm down. (It is very hard for her to tell you that you are calm and happy!)
Also saying you will be gone for a finite period of time (and sticking to it) can help. Leaving can/will trigger her fear of abandonment, and if she knows you will be back in 20 minutes or 2 hours, it won't be as bad.
Hang in there!
GK