>someone who's been betrayed but has never betrayed, someone who has only tried for lifelong commitment but was let down
Uho! Inferiority complex ahoy! The need for women with low expectations... That doesn't bode well for you. Please mature, >>6-san. (And no, maturity has nothing to do with sex).
>Her past gives away your future.
Downright false. Her past INDICATES a possible future. However, I know plenty of people, men and women alike, who had similar pasts to OP's gf and then later happily settled with partner. People grow, people change. Small changes, big changes - time affects everyone.
>Hence if she can't be sexually satisfied, there's no guarantee she won't cheat on you with this mindset.
This is why OP needs to clearly discuss such rules for the relationship with her, and be aware of that rules don't have to be cast in stone, though it's perfectly okay to demand certain rules be perpetually followed for the relationship to still be valid (also, make sure about what constitutes as cheating, different people have different ideas - some consider casual no-strings attached flirting cheating, some don't consider anything below sex cheating). Perhaps the two partners will grow apart later, perhaps not. It's important to try to not take a possible fall-out too personally.
Also, if both partners are openminded and exerimental, and don't have some sort of retarded "pride" in bed ("Oh noes! I didn't perform perfectly! That must mean I've shamed myself! Shame shame shame! Now I must behave oddly and distanciate myself!"), there shouldn't be a problem with anyone being satisfied. Casual sex is casual sex: It's fun, but really awesome sex comes from being with someone that actually means more, that makes your mind tingle with happiness and love. That kind of sex is a lot more worth than "just" sex.
Also: Sex is fun, and so it's important to be able to laugh in bed. If something doesn't go as planned, be amused at it, and don't let that stop you two from being happy.
I second >>16's >Better to have loved and lost than never loved at all.
It's painful when you lose people, but it's a learning experience. Treasure the good moments, learn from the bad.