there isn't a way
If he truly wants you back, then of course!
If you want your boyfriend back, who is currently with another girl, simply approach the other girl and tell her to stop spending with your boyfriend.
If he wants to marry another girl he's not your boyfriend.
you're an idiot for takin' him back. you're an idiot for takin' him back. you're an idiot for takin' him back.
It's been a year. Does his new girl deserve an ex trying to take her boyfriend away? Get over him and find another partner, or even a hobby.
Get another gye that really cares about you. Seems this boyfriend couldn't so why be with hime if he cheated on you and doesnt love you. Gte with another gye and make him jealous.
If he's just a friend to you now, then you don't want him back.
if the girl he is with is being nasty or treating him badly for no reason that's acceptable, or if she is talking about an ex or another guy she thinks is cute just to get back at her boyfriend.
You don't.
If your married divorce him, if he is your boyfriend DUMP him.
if i where you i would tell the girl that likes that boy that he has a girlfriend.that is what i would do.