Hi. My boyfriend and I go way back. He used to be my best friend so I know all his dirty little secrets. He has an history of being unfaithful to his ex-girlfriend, but he was my friend, I didn't care. Now I'm the girlfriend, and he says its different but still in the back of my mind... I had the habit of reading his text messages before we were together, but since we started dating I get mad about some things I read. He says they're normal, that I'm just being jealous, and I used to think they were normal before, but now not so much. In order to don't fight anymore I stopped reading them. Now I'm affraid to read them and discover something unpleasent. Is it normal to be affraid, or am I just in denial?

Give him some privacy. There's a line between married and in a relationship.. don't pretend like you're married to him.
If you keep on reading text messages, he might end up being really upset, and that could cause more problems in the future.
Thanks :)
But I am going to just assume he's flirting with other girls via text. And you have every right to be upset about that. I'm a guy and I don't find interest in texting a girl I don't have interest in. He's not just texting other girls because they are cool and have a bunch in common with him. They probably have little in common with him actually. He's texting them because he's enjoying the flirtatious attention from other women besides you. And since you are his girlfriend, his behavior is not right. You shouldn't be with a guy like that. There are billions of other men who will cherish you like no other. Trust me.
I'm afraid of reading his messages because I might find some texts out of context and make a big deal out of them. I just wanted to know if this is a normal feeling for everybody, or if its just me.