<human>: Or for those of you who don't believe that teenagers can love, then this is love as I know it, at this point in my life.

My girlfriend and I have one huge discrepancy in our relationship, which is that she could see us being together for the rest of our lives, while I can't see us lasting past high school. She honestly believes that she will never find anybody better than me, and she never wants us to break up, ever. She knows that I'm not on the same page though. She knows that I don't want to do long distance after we graduate, and that although she's my first love, she will not be my last. And because of that, and because of the fact that she knows that eventually, I will break up with her (because we both doubt she'd be the one to break up with me), she can't believe me when I say that I love her.

It puts me in a really awkward situation; in all of my failed friendships in the past, it's always been the other person who got sick of me and stopped talking to me. It's always been me that's left to beg for them to forgive me and I'm always the one who has to work for other people's friendship. In our relationship though, she's the one who's terrified of losing me. She's completely dependent on me, to the point where it's a little overboard. But she absolutely cannot believe me when I say that I love her. She knows that inevitably, we will not be together someday and it terrifies her. So every time I tell her how much I love her, she thinks that I'm saying it out of pity. She thinks I'm only still with her because I pity her. But I really, truly love her, and I just want her to see it, because right now her negativity about it is kind of degrading our relationship. How do I make her believe it?

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: My girlfriend finds it hard to believe that I love her, because she knows that someday I'll break up with her. How do I make her understand how much I care about her?