I don't go out on dates because there are people more deserving of a loved one than me.
What makes you think others are more deserving than you?
For starters, there's a girl that I like that rejected me because she's interested in someone else.
It can be easy to get bogged down with insecurities when you're dating, but you have to remember that everyone has things they're insecure about but they press on anyway. If you let your insecurities dominate you, and then it'll be all the more difficult for you to find a relationship. If you can't find it within yourself to be more confident, then you may need the help of a therapist.
I know that she's going to be with that guy she likes over me because I am a loser. No therapist can help me with that.
I know that you want girls to like you but it is your self-doubt that is really what is getting in the way and it's not good to see yourself this way. A counselor could absolutely help you with this issue if you would just give them a chance.