I hate to be the bearer of bad news, but I've had several cysts pop and one was triggered by sex. (Please note that I am NOT trying to scare you.) My boyfriend and I had sex in the early evening, and it was a little uncomfortable for me, but not exactly painful. Afterwards what was an uncomfortable feeling slowly turned to pain and got worse until I passed out at about 1:00 a.m. and was taken to the emergency room. They diagnosed me with a ruptured cyst. (There was no bleeding, so I'm not sure what your friend experienced.)
Now I believe that this was an extreme case and in all the years I've had cysts rupture and been having sex, this is the ONLY time it happened because of sex, and it was by far the most painful cyst I've ever had, which had nothing to do with the sex. (It was the only time I ever fainted.) I do NOT think that you need to be afraid of having sex, but it IS possible that sex could trigger a rupture. But it's not like throwing darts at a bunch of water balloons when you have sex--my cyst had to have been close to rupturing anyway, and the penetration just helped it along.
Bottom line, if your cysts are going to pop they will do it with or without sex. Sex can sometimes just "help out." It sucks, but nothing you can't live with. If you've never experienced a ruptured cyst, they may sound a lot worse than they actually are. They definitely hurt, but we're women! We're made to withstand pain.

And it's only happened to me every other year or so-it's not like I'm continuously in pain, thank god.
So don't sweat it. Chances are if you do have cysts then you've had them for a while, and sex with your boyfriend hasn't affect them so far, right? But if after sex you're feeling some lasting pain in that area, that may be what it is, so don't freak out. But you said that you're on BCPs, which for me is what keeps the cysts at bay. As long as I'm on birth control, I don't get them. That may not be true for all women, but it's worked for me.
Sorry if I scared anybody!