HI JStarr,
Sorry to hear that your relationship has been so difficult lately. I can imagine how scary it is knowing that your partner makes threats to your reputation.
It's important that you do have a social life and there is nothing wrong with you wanting to go spend some time outside of the house. Often pwBPD have a fear of being rejected and friends are seen as a threat to the relationship. One thing that I've found helpful is that when I have social events coming up, I make sure that I
validate my H's fear of being rejected first by saying something like "It's important to me that we spend time together. A friend wants to go out to dinner on Friday. I'll be home around 8pm and when I get home we can spend the rest of the evening together." See how I made sure that he knows he is important to me first BEFORE I let him know about the social event.
How can you take the fear out of those threats? Do you friends and family know that you do not do drugs? If the people who matter to you know that is not the case, then would her accusations of drug use REALLY harm you?
Can you keep track of dates and times that she makes threats to you, including the argument that led her to threaten you? Don't tell her you are tracking them. Just keep it somewhere safe for future use if necessary.
IT sounds like you are being controlled with
FOG . FOG = Fear, Obligation, and Guilt. Getting out of the FOG could help you get some clarity into your situation.