I am so Insecure, I don't know what to do anymore...?

This is driving me nuts! I don't think I am ever gonna be happy.. because of this. I got with my boyfriend in November 2009, I never had self esteem issues when I was with him, we used to watch porn together, I used to comment on other women with him and say they were fit, I didn't even care about watching t.v with naked women in or him watching porn on his own, or even looking at a nude mag. I think it all started in march 2010, 4 months into the relationship, I lost my virginity to him four month into the relationship, I don't know if its because I'd become sexually active with him and I started to think it mattered what he thought of me. I can';t even watch t.v with him without panicking a sexy woman's gonna come on the .v or film scenes, knowing hes gonna be looking at them, I get funny when we walk down a shop isle and there's nude mags on the shelf, I kick off if he looks and all these things start going round in my head, all these thoughts, when were walking round town or out and about say in the pub or on a night out, I'm constantly watching him to see if he's looking at another woman, and if i see him do it i go mental, and that automatically makes me ruin the day, I cant believe how bad I've got, Its actually bad that when a song comes on the music channel with women practically naked I get really insecure.. When he goes out to town on his own, with mates, i know he would never cheat on me, but tats not what i worry about, I worry about where hes looking, and say with pictures people post online, i get panicky over what hes looking at. Now there's another problem that makes it a lot worse, hes planning to go abroad with all his lad mates which are single.. Magaluf, I believe that that's a place to go when your single and you wanna just go wild, that's why they name it "shagaluf" and "shagamuff" now don't get me wrong, I don't hate myself that much, I take pictures a lot, i think I'm a very pretty girl, i am quite slim and I'm a lot skinnier than when we i was when i first got with him, I do think I'm really good looking, but when i get around him, i just don't feel that good and think hes always looking for a better prize, Has anyone got any TIPS at all to help me and make me stop all this insecurity, because I don't think I'm ever gonna truly be happy, I love him to bits, but I just cant keep living life like this, worrying everyday! its driving me mad, and I hate it. No matter how much weight I lose, and gain a nice body, nothing changes.. I just think I'm gonna be like this forever, I've always said, well maybe relationships are not for me, But I don't want to be lonely for the rest of my life just because I cant accept that men Look elsewhere.