I don't trust my husband on the internet?!?

I have been married 5 months, but I've been with my husband for three years. Just recently my husband started working nights, so his sleep schedule is opposite from mine. He stays up late and is on the internet alot. (It doesn't help that I go to bed by myself every night) Well, the other day, he forgot to log out of Facebook. I noticed where he had messaged this girl saying something like "I saw you the other day and you looked pretty hot"... and another girl saying "you look pretty in your profile picture" and things like that. It BROKE MY HEART and made me feel so crappy. He watches some nights. I've seen where he has browsed personals. I HONESTLY don't think he would ever LITERALLY cheat on me... I think he does alot of it out of curiosity. But this bothers me GREATLY... It upsets me just like if he was cheating on me. I find myself browsing our history and trying to get into his e-mail constantly. He deletes the history because he doesn't want me to know what he does, because he knows it will upset me. We live in a small town and I ran into this woman the other day who approached me and said "Oh, are you ____'s wife?" because they had messaged on Facebook! It is so embarring to me that people KNOW how he disrespects me! I've confronted him once and he said he was sorry and wouldn't do it again... but I still worry about it and I don't trust him. I honestly don't know what to do. I hate to keep bringing it up to him, but I feel like we can't fix it if we don't talk about it. Maybe it's my problem now... am I just insecure or is it normal to be hurt by this?