“You must not commit adultery.”
-Exodus 20:14, NLT
All sort of horrible things may have happened to a cheater in his or her own past. Their family of origin might have made the Adams’ family look like a picture of normality.
It does not matter.
God does not give out permission slips to commit adultery for having a rough past. He did not say, “Thou shalt not commit adultery unless you had a rough past.”
Now, I hope every cheater with such a rough past deals with that past in a constructive way. That means attending therapy and working through spiritual issues with a pastor.
It does not mean cheating on your spouse!
You do not get to abuse another human being just because you were abused. Being sinned against does not give you the right to sin against another.
And make no mistake:
For faithful spouse, I would encourage you to keep this truth in mind. The cheater may have been responding to sin by choosing to sin against you. But that choice was still sin on their part.
And they are still responsible for choosing to respond to sin with more sin. They could have chosen otherwise.
You are not responsible or liable for their wicked choices. They alone must own those, and hopefully, repent before it is too late.