How can I trust my girlfriend again?

[MynameisJesus]

^ She's 20 years old. The odds that she will sleep with 4 more guys in her lifetime before settling down to "the one" and get married are very high. I believe the average number of sex partners a female in North America will have in her lifetime is something like 8-10. Generally a girl is less likely to settle and marry her first love that she met when she was 18 yrs old. My statement only suggests that the OP needs to let her go and explore, because if you don't....her curiousity about other guys are just going to build up and she will cheat behind his back. Perhaps when the right time comes again, if it was meant to be.....the two of them will find each other and hit it off again.

I agree with all that. For some reason being cheated on evokes a lot of emotions in me.
I hope some day I can reach the mindset that allows me to not care about my girlfriend/ wife/ partner or whatever f^cking an other man.
At this point I could never take someone back after being cheated on.
" It was meant to be " is one of those lines that makes me frown. It was meant to be with so many people. You just run into very few of them

[bcgirl]

^ I understand where you are coming from. I am the same way.... I've broken up with my ex boyfriend 3 years ago and couldn't imagine getting back together with him because I wouldn't be comfortable knowing how many women he's slept with in the past 3 years....although it wouldn't be considered cheating if you sleep with people while you are broken up. There are tons of people that break up and several years later find each other again and end up getting married.
I also understand where the OP's gf is coming from. I was once 20 yrs old too....I was in a serious relationship but needed to explore my options before getting too old. I was in love, but how could i know if he is "the one" if i couldn't test other men. We broke up and I did test other men, I am very grateful that I did because it gave me the experience I need when it came time to settle down. I am now happily married (not to my ex).