I'm mad that my ex best friend ditched me for an asshole.
Why do you think that they ended up ditching you?
Because he realized that he can do better than me
While it is understandable that you are upset at your friend for ditching you, you shouldn't think so lowly of yourself that your friend ditched you because you aren't good enough. It would be a good idea to talk with a therapist about your self-esteem and self-image and learn ways of thinking about yourself in healthier ways. With good mental health and a positive outlook others will be attracted to you and will want to be your friend.
I'm going to try talking to him. I already see myself in a better light.
I think that you should try to find some new friends though. You should not feel that you are lesser than the people that you are around.