Am I crazy for being this jealous?

I hate to see him with another girl even though we aren't together for over 6 months. i feel a deep burn when i see him with another girl dating or anything like that. i know this might probably scare you because ofmy jealousy but i just love him to much, every time i see that he is dating someone i feel a deep disapointment down to my throat of what i had done. how I ruined the relationship that everything was my fault that I had done EVERYTHING. I feel like i will never be happy without him. I feel like he is the only one. i feel like im going to tear apart if we don't get back together. I always give advices to his gf because we are friends. I know him so well and everytime i help her it works and everything goes back to normal everytime. I am the one who built their relation ship! i hate myself every single minute that i am helping her when i should be helping myself getting back with HIM!