I'm sorry, but if you cheat on me, that's because YOU made the decision to do so. I don't care if the relationship is strained or not.
"Strained" means something(s) is under pressure before the cheating. I cheated and it didn't just happen. There is nothing I can, or will say, to try and make it sound OK. It's not OK and it was an awful and dreadful harm I chose to inflict on her. However, the strains on our relationship made it inevitable, to which I bear enormous responsibility, because the strains were not being relieved or addressed and that wasn't all my fault.
To the question, cheating isn't the issue, in my view. It is a symptom. The illness is all the underlying strains. As such, focusing on the symptoms and not the 'disease' misses the point. Sneezing and coughing and runny nose, headache, so to speak, are the cheating and all bad enough but, they are expressions of the underlying illness. Is it just a cold? Flu? Poisoning?
I suppose there are people who cheat in otherwise healthy relationships and I know some guys who it's simply understood that, on occasion, they're gonna do what they're gonna do and the wife just accepts it, especially if she doesn't have to see it or hear about it. But, in those marriages, it's more a deal and that is not for everyone.