Depends on circumstances. keep in mind classic female fukkery is to get with her ex's best friend to rub it in his face. Got to make sure he tossed her in the bushes and gives zero fukks.
If he still wants her or can't stand being around her then
EDIT: one of the WORST violations of Man Law I ever saw was my freshman year in college. Nerdy breh goes to college with his highschool sweetheart and she's hanging in the all-male dorms just about every day with us. She's starts flirting with an "upgrade" and after a few months, dumps nerdy breh for this dude who gave zero fukks about anything but regular p*ssy. So, dude has to sit with us in the dorm lounge every damn day while his high school GF is hugged up on a dude who talks shyt on her the second she's out the room.
Man, seeing that dude transition through all kinds of emotions over that semester.