I think you should dump his ass and find someone who will appreciate you. Why? You're only 18 and are in a relationship which is close to being similar to a long distance relationship. For me liking other girls pictures and creeping on them is acceptable in the early stages of dating and when you have been going out for quite some time, like 3 years. You say you are in a trusting relationship but the fact things could start to turn sour when you begin to compare yourself to these other girls and why does he like them and not you which will breed insecurity and lack of trust driving you crazy. Child you are too young to even go down that road yet. Be young, single and fabulous now while you still can!