Very confused over relationship. Help!?

Ok well first off, I know I am a sick person so don't say it again. I went out with this girl for like a month and we were truly in love until one day someone told her I was cheating on her and SHE BELIEVED IT!!! She dumped me immediately after when I really wasn't cheating on her. She became very depressed. I tried to tell her but she wouldn't believe me. This made me very upset that she would even think that I would cheat on her so I created this overwhelming anger towards her. Now to get revenge on her, I am going out with her best friend. I know she feels deeply depressed but in a sick way, that makes me feel good inside. Someone talk some sense into me. I don't even know that I like her best friend but it is the ultimate retaliation. In all reality, I am just going out with her best friend for emotional stability. Please help.