Ok i need help from both guys and girls seriously?

Im dating this guy and i love him very much hes never given me a reason to not trust him so of course i trust him. We started dating in Oct of 08 he had dated this girl i knew about a year before i started talking to him i had only seen him with her once and i didnt kno him back then. Well the girl and me are basically enemy's she hates me i hate her we have our reasons but we still kinda talk when we wanna. Well when i started to date my bf she was mad. I asked my bf about her and he said they hadnt talked in a long time and he never though about her. Well last night i was looking on his computer he wasnt there and i ran across some old ims between him and her and these were sent like 2 weeks before me and my bf met and started to date. The ims were about how he loved her and how she loved him and how they wanted to have in detail he had her explain to him what she would do and he told her what he would do also about how they would send pics to each other but he told me he never sent pics to her she only sent to him i couldnt keep reading it made me cry why would he lie to me and say they hadnt talked when they had only a few weeks before me and him met. It scares me if he lied about that could he be lieing about other things? What do you all think i should do? How could he love me when he told her he loved her i just dont understand.