Am I the only one who feels like this and how can I get over it?

Have you ever liked a guy and then you see a different guy and think ooo he's cuter maybe I should hold off until I find someone cuter? I feel like a horrible person when I feel like this but I can't seem to help it. I think I'm just scared of committing to someone because I've been hurt before and I think that's why I feel when I see someone cuter then the guy I like that I could do better? I just dont know. Is this normal? Has it happened to you before?