I have BPD and my biggest struggle is with FP. Because this has been such a big issue in the past with SOs I stopped all romantic activity for almost a year. I refused to feel anything about anyone, and it worked. But then I met new boy and everything changed. 
We hit it off immediately, I have been extremely transparent that I do have BPD and he’ll end up being my favorite person. Spoiler alert: We had sex and he did! 
The week after we did it I was an immediate “he hates me he’s going to leave me conflict” and then last weekend when our plans didn’t work out I had a bad meltdown. This did nothing but completely overwhelm me with feelings of abandonment that I ruined everything. 
Luckily that was not the case. I have centered myself now (too little too late, didn’t finish any of homework due in 3 hours.) He is extremely busy and works 12+ hours a day. He needs his space and doesn’t feel like texting all the time. But even if I am calm now, or at least not manic, I’m still in paranoid freak out mode that he is going to leave at any second. 
Having sex with someone I am interested in seems to be a gigantic trigger for me too... 
Does anyone have any advice on how to be calm and rational- I don’t doubt he likes me. My BPD says otherwise. 