Why am I so scared of losing you, when you’re not even mine?

Because of a friend of mine (ex-ex-boyfriend), I'm really messed up. I have a real hard time trusting people, and I'm always suspicious, I mean, don't get me wrong, this way it's harder to get heartbroken, but this way, I dont' really enjoy being with someone, because I'm always looking for reasons to end it, not that I want to end it, but I know that someday it will end, and so, I prepare myself, in a way. 
And, right now, I'm sort of in a relationship, and because of all the crap he has pulled, I'm scared of getting too involved in this, I'm scared of letting him in my life, yet once again. Very few people know we're dating, and so, his friends are always talking about this one girl... Apparently, he told'em that he's in love with her, and when they told me that I freaked out, who wouldn't? I asked him point blank, if he was in love with her, and he said no, he said he liked ME, and I feel in my heart, in my gut, he's telling the truth, but my brain just goes back to cheating, goes back to all the nights I was awake because of him, all the times I cried when he passed me by, all the days he didn't talk to me, and I don't know what to do... Because no matter what, I'm always going to be like this, I can't help it, because even though I know he's not the kind of guy that cheats, I'm so tired of listening to his friends talk about her, and all the handshakes and the Wow's because of her, I'm really starting to think otherwise, and I cannot talk to him about it, because I'm scared, and I don't know how long I'm going to have to put up with this, because, yes, he has shown me that he cares about me, but he has also shown me that he doesn't, and I don't know in which I'm supposed to believe in... 

Everytime you talk about her, I listen with my fake smile, and I can hear my heart break and I can feel it being torn apart. Because it's in those moments that I realize that you've never talked about me like that...