Please help! I need advice on my relationship~

Tamarra
I've been a relationship with my boyfriend for almost a year. 11 months to be exact. Right now we are having some problems. We both have an odd feeling that our relationship isn't how it used to be. It's just an odd feeling I don't even know where it came from. He's told me he doesn't want to break up because he loves me but the feeling we both have can't be avoided. We've been having serious talks frequently that just leads to more problems. 
I've admitted to him that I've been having pent up anger because he just told me there was a friend of his that's a girl that he had class with and thought I'd beJealous. I told him I don't care but I kind of do because I know that girl sleeps around with guys and was apart of a guy cheat on his girlfriend. I know he's never cheat on me but it's just in the back of my head. He doesn't even talk to her a bunch only when they have class...Once I got that off my chest I felt that we were ok...but recently things still feel the same way. 
I dont know what's going on and want everything to go back to normal.  
 We one has sex and he told me he didn't feel anything like how he used to and totally felt the same way. Then we talked more and we both felt the "spark" once again but now it's like it's gone again. 
Any ladies that have been through this in some point in their life and fix it. Do you have any advice? Im so worried and I don't know what to do. Absolutely we love each other but we don't know what's going on. I don't know what to do. 
We just came back to college from summer vacation and we thought that we'd be so happy once coming back but now it's just....odd...