YABU
I can agree that sometimes cheating happens on the background of a failing/unhappy relationship, rather than in a vacuum, BUT if you are unhappy for whatever reason and/or find someone else, then a decent person will end the relationship before cheating.
Cheating isn’t just the physical act, it’s the lying, the concealment and so on that goes with it. I’ve been cheated on. It hurt, it damages self-confidence and trust in yourself and your judgement, it damages your trust on other people. It is a horrible, shifty thing to do. There isn’t really a good justification, other possibly being in an abusive relationship (but then I still think you’d be better off ending it for that reason that cheating). All the “but we weren’t happy”/“I felt emotionally neglected” etc might be the reasons why you were tempted, but they are just excuses- if it’s bad enough to feel justified in cheating, it’s bad enough that you should end the relationship before you cause harm to someone you once cared enough about to have a relationship with.
it’s not about hero’s vs villains, and you are right life is not straightforward, but we can all choose how we behave and the actions we take. Cheating is a choice you make. There might be reasons as to why you are in the position where you want to, but you don’t have to do it, you make the choice to do so. And it is a shitty thing to do to someone, even if you no longer care for them as you once did or are angry with them, or hurt. It’s the difference between having integrity and lacking it.
I say again- if you are unhappy then address it and work on your relationship- or if your partner won’t agree to that/pays lip service to it, or you feel the problems are unsolvable, then you end the relationship.