Honestly lost

I've been with this guy for a year now and I've had a crush on him since high school, so 6 years now, he was with one girl for 4 and it's been 3 since they broke up, he still loves her and wants her. But how he feels for her I feel for him and I know I should leave but I can't...this is the second boyfriend to so this to me(be obsessed with their ex) I don't know what to do