Cheating? WHO DOES HE LOVE???

I found my man's journal I know I shouldn't have but I peeked in. We've been together almost two years and he tells me he wants to get married but in an entry he talks about his ex roomates gf and how he fantasizes about her sometimes when he has . In the journal he talks about ways to get rid of these fantasies and it seems he is upset over them. I know before we dated he liked this girl and so he never calls her back or talks to her anymore(better not lol) but does this mean he loves her? Before we got together his entries were very jealous of his roomie saying he wish he found her first etc and from the sounds of it they were friends up until he started getting serious with me. Should I be worried? I am PISSED and jealous idk what to do. He never talks about her to me but his journal is filled with crap about how he misses talking to her and wishes he could see her again etc. It bothers me. Oh also he is 30 I am 24 and she is 21. I admit I did dig through his stuff we live 2gethe