Why do I get so fking jealous of my ex-friend?!?!?

Don't stalk her Facebook... It's unfortunate that you cannot control the jealousy, but since that's the reality of the situation,and you have already chosen to quit the friendship, just move on. Whenever you catch yourself thinking about her, shift your thoughts to something else. Make a list of somethings that are great about yourself. You are at least a good enough friend to not want her to be hurt my your jealousy! Do some positive self-talk. Really, it helps even though it might feel dumb or pointless. Give yourself a compliment everyday and that will build yourself-esteem up! Once you gain the power of great self-esteem, you will no longer feel jealousy because you will feel adequate and happy with the person you are!