Why do I keep having dreams about me losing the females I've liked?

I had a dream this morning about me losing a girl I currently liked for a while. I lost her to another guy. Well, guess I never really lost her since she wasn’t mine to begin with, but I felt like crap in the dream. And I was unfortunate to wake up feeling the same way. This isn’t the first time I’ve had a dream about me losing a girl I’ve liked to some other guy. This happens to reflect current events in my life now, but why am I dreaming about it also? I’m a really nice guy, and I’ve never hurt her. So why?