Me being the happy pervert that I am, I'd normally suggest that you just go with the flow. Hey it's better than masturbation right? However if I were to be completely serious I'd suggest just staying friends with her; no "benefits" or anything. You two being sexfriends might cause some emotional tension. It's almost impossible to keep a friendly relationship with someone while having sex with them unless you are emotionally desensitized. But hey that's just my opinion. You could always take my first option into consideration.

tl;dr: DO IT FAGGOT