Public Service Announcement:
It was NOT your fault that they cheated on you, and it is not your job to make them faithful!
I want to encourage you that they need not buy what others sell regarding infidelity. They might try to make you feel responsible–if only in part–for your cheater’s actions. To take that on would be to believe a lie.
Namely, “The Shared Responsibility Lie” is what such people are selling. This lie says that you are responsible–even “only” a little–for another’s sins. It is a lie.
Do not believe it.
Remember:
It was NOT your fault that they cheated on you, and it is not your job to make them faithful!
Your partner is responsible for keeping their vows to you to be faithful. That is on them. Not you. And it is also on them if they fail.