Boys!

So I dated this guy 3 years ago for 9 and half months then we broke up and become off an on again kind of relationship well this year we both slightly moved on, I'm really happy in the relationship I'm in right now with my new boyfriend. I really really like him, but every time I see my ex (he is single right now) I really just want to tell him that we should get back together but I know I shouldn't. All my friends say if I leave the relationship I'm in right now for him they would never talk to me again. I don't want to leave him but at the same time I still really like my ex Someone Please help.