Thank you to everybody who replied. Especially >>6-7, who give interesting thoughts.
To tell the truth, I tend to exaggerate when my mood swings. I wasn't being completely honest in >>1. The real reason I haven't broken up with my girlfriend yet is that I don't want to. Because most of the time, I absolutely do love her and could not live without her.
However, there are times where I feel exactly like I do in >>1, and of course I was going through one of those times when I made this post. At these times, which can go on for days, love seems a dreadfully foreign feeling to me. And that is when I start to question why I bother staying with her when I'm so tired of her.
But once my head clears, I'm all over her again. Maybe I'm over-complicating matters by thinking too much. Should I really need to expect anything more from her? Perhaps I need to learn to just relax and be content with her existence complementing mine.
Maybe our relationship is doomed because of the times I feel like I do in >>1; maybe I can get over it. But I'm going to hang in there for now.
Sorry for being somewhat of a liar. It's just how I honestly felt at the time.