Bro, you don't have a trust issue. You have a real issue. It sounds like you don't trust her because she is untrustworthy and has done multiple bad things to hurt you in the past. Distrust, when justified, is there to keep you safe.
A "trust issue" is when you don't trust someone for no reason. i.e. your GF is unreachable or out with her friends and you think she's doing you wrong, cheating, when she is not. You don't have a trust issue.
For example, justified: I distrust pedophiles, currently addicted drug addicts etcetera, because they are likely to re-offend.
My advice would be to have fun with her, enjoy her when you can, but don't spend one more day thinking about a future with her. Do your thing, find another girl/girls, don't sweat that she may be with someone else sometimes. It happens and you can't stop it. So either bail on the whole thing, or back way up emotionally and enjoy her friendship and the sex.