If I convinced my bf/gf to leave their spouse, will they ever return back?
Title said it all.
Forum Discussion
Probably not, when a Sims leaves another Sims they get pretty upset.
If you mean will they still be in the game. Then yes they will but as @Phantomlover1717 said their relationship will have taken a severe dib. It is unlikely that they will recover enough friendship to get to be girlfriend/boyfriend again even if you decide to break off your relationship with the sim.
