Do you think i can trust him?

Ive been with my boyfriend for 3 years now, and ive always had issues with trust as ive been hurt in the past before and im insecure about my looks. Well we have had arguements in the past where ive found messages to other girls on his facebook and phone calling them babe and telling them they look stunning and he has reassured me it was nothing and just friendly, i had no evidence or reason to believe otherwise and it got left at that (that was october 2010), Anyway .... i asked to borow his phone last night and when i unlocked it, it was open on his messages from a girl saying things like " ok babes are we going for that drive tonight" and things just feel dodgy, i had a quick check through his phone this morning while he slept so i could check i got my information right before asking him about it and he had deleted it! I dont know what to do i love him so much. I also noticed on his phone that he met her the other night when he finished work (he finished at 10:30 got home at 10:50) and said he got caught up at work thats why he was late. Im so worried that something is going on but would like some advice form impartial parties as everyone that knows us says "he would never do that" but all these messages say otherwise, especially as he knows it bothered me before and said he wouldnt do it again, i just feel like im not good enough! please some friendly advice ... thanks in advance xx