What would be the best way to handle a situation in where I hate the guy my best friend is dating?

Ok so me and this guy met and we really hit off. We both liked each other..until I introduced him to my best friend and then they fell for each other. I was really hurt at first but we all managed to become really good friends. But then things started to go down hill. Me and the guy started arguing all the time over everything. He would always get mad at me. Me and my best friend also started arguing alot because of all the problems. So finally me and this guy decided to not be friends and to never talk again. This is causing alot of problems between me and my best friend and it also hurts to lose him as a friend. What should I do? Any advice would be great..