I'd say it's normal for our age (I'm turning 21 in a week!) especially when BPD is in the picture since many of us greatly desire intimacy. I personally have a very hard time opening up sexually part of it was past abuse, but I think a lot of it has to do with my anxiety over becoming negative after sex (all the chemical releases) which has happened a number of times, even if the experience itself was enjoyable. Ugh, curse you mood swings. I wouldn't worry too much!