Should I break up with her? It's her birthday!

So, this is kind of a long story so I'll do my best to shorten it. I'm 15. My girlfriend is as well. About a year ago, her cousin was dating my best friend. I was good friends with both of them but when they broke up, the cousin manipulated me into thinking my friend was a horrible person. I completely cut him off, and began dating my girlfriend shortly after. At first, things were great. We share so many interests and have a lot in common. But it's getting to the point where she wants to talk on the phone with her for hours on end with nothing to actually talk about. She just expects me to carry the conversation. Things are getting boring. We've talked about the same stuff for so long and it's really lost it's charm for me. I find myself avoiding phone calls entirely because of how boring and awkward it is. She's also WAY more attached to me than I am to her. Not even a month after we started talking... Let me say that again. TALKING. Not even dating yet. She was already telling her cousin that she loved me. And she still does. I've said it but I've stopped because I realize that I don't feel the same way. With her feelings toward me, she's also getting kind of clingy. We got into an argument about how she doesn't thin I care about her at all, because even if I did want to talk as much as she does, I can't with my extra curricular activities at school and stuff outside of school. I've recently started talking to my friend and he tells me that this is exactly why he broke up with her cousin. If either of them find out I'm talking to him after all the things I was made to believe about him, they'll make me look just as horrible as him. I want to break up with her soon. I don't want to deal with the stress coming from this any longer. But her birthday just happens to be coming up in about a week and a half. She's expecting me to go so I can meet her parents who she hasn't even told that she's dating me. She also lives in another city so texting and phone calls are our only way to communicate most of the time. I don't know when to do it... Should I do it before the party and possibly ruin her birthday? or should I do it after and fake my way through it? I've felt this way for a while and I intend to tell her that. How should I do this? And should I cut her cousin off too after what she did? I'm feeling really stuck here.