As the spouse to a serial cheater, what if you aren't the victim but...

[Believe_N_Me]

...the old husband who forced a young woman to marry you and trapped her to stay with you, like in "The Crucible"? lol

Okay, I'm not really sure how you can trap someone to stay married to you, but there are people who can manipulate their spouse to stay. Don't ask me how because it's different in each case. Maybe you control the finances, you have dirt on them, they owe you a huge sum of money, your parent is their aunt/uncle, etc. Whatever the case is, maybe you're the one holding them back from seeking someone they could actually love and want to be faithful to. The point is, they aren't faithful to you anyways.