Is My Boyfriend Lying To Me About Her?

Me and my boyfriend have been dating for 2 years and 4 months, we had some troubles here and there but we always got through. Now he moved away from me one year ago , and now he is 3 hours away. he would occasionally visit sometimes and i would see him if i ever got the chance to go. however, i went through his emails while we were in the mist of a bad argument, and i found that he was talking to two girls from his school and was flirting with them and one of them were flirting back...thing is, he is turning 18 about to be a senior, and the girls are just turning 15 and going to be sophmores...i am 17 and going to be a senior as well and i will turn 18 soon...but when i talked to him about them he totally denied it till i told him that i was talking to the girl and then he admits it...but he wasnt in no rush to fix things...not to mention, those girls looked very similar to me, same attitude, i felt like i knew them as my younger self...i thought he was confused...but as of now, we are patching things up, but occasionally the other girl seems to have gotten interested in him and he always likes her pictures and tells her shes cute...but he tells me he doesnt like any of the girls anymore, and that he loves me...and he has began to start doing sweet things for me, like making a slideshow with all the pictures he ever took of me and tells me he loves me and that im beautiful and he wouldnt replace me cause no one could be me...but since im not there with him, i dont know what to do. he stays home more to tlk to me but ... im still scared to trust him.