Hello! I wanted to recommend the fic My Love Paramour by Ambienthands
It's a morally grey fic, agreed, but as someone who's been through abusive relationships, it's an accurate representation of how abusive relationships often leave you with less ways to escape and leave you scrambling to find comfort however you can. I'm not saying cheating is right, again, but the fic shows how sometimes morals aren't black and white. It's worth a read, I think.