I cant seem to trust my girlfreind?

its kind of a long story ill make it short.so ive had this previous girl and to make it short she put me through hell she lied to me cheated right infront of my face and ever scine then my trust has just dropped well i have this girl and she totally opposite shes really smart takes AP theory classes really smart really honest.and well shes beautiful lol so there's alot of guys that like her but they dont act on it.and well today she went to this teen club she said she wasnt gunna do anything at all we've talked about this like over 5 times.and i still cant get it through my thick skull.idk what it is i just cant trust her i love her so much.idk i need help what could it be?