i wanna try pse but i wonder is it safe and how do i know if it safe r not thanks

Do not expect bbfs.  Otherwise, why would you be worrying if it's safe?  If you have seen the girl in movies, she may or may not do the same things with you that she did on video.  Do your research on her, like reading reviews to see what she does or does not do in her PSE sessions.

Swim

PSE is not bbfs, if that's what you're thinking . It describes the date, may include cof, bbbjtc nqns, greek etc.  Read the porn star board to get more of a feeling.  And yes, it helps if the lady has movies. Even though, non pse providers offer pse.

...or a recurring back spasm.

PSE has, in some circles, become shorthand for uncovered FS, often at an upsell.
Even though you may remain covered, you do not know whether or not she makes this a regular practice, and it may increase your risks.