Right relations

I feel like I can never be vulnerable or intimate with anyone. I cheat and always feel better off with multiple partners but deep down I want to be able to have lasting connection with someone. I want to have better relations with people in general. I am nicest to strangers. But I can't keep good friends for long. Especially girl friends. I wish I had a better relationship with my best friend, I wish I was there for her when she needed me. But now it feels like she competes passive aggressively and  tries to make me jealous with friends she has (she lives cross country) and the success she is having. Or maybe I just see it that way because it's all on fb anyway it's not like she texts me going "look at me I'm happier!" But I couldn't even tell her when I got my heartbroken for so long after it happened. I had to get comfort from my ex. Who I cheated on and left for the person who broke my heart. My ex has unconditional love for me but I treat him like shit. I am so cold. So mean. I don't want to be. It's horrid. If I saw a video of myself and the things I say to him I don't think I would be able to love myself. Maybe that's the underlying problem is I need to love myself so much that it would hurt me to hurt others so. It should. It does. I'm only becoming aware of it. How do I cultivate right relations in all aspects, love.. Family and friendship?