Why is cheating accepted ?

I've noticed a theme with cheating and affairs. Women cheat as well, I'm aware. However, it seems to be a common thing where married men have affairs, wives work on forgiving them, boyfriends cheat and some girlfriends give them 2nd or 3rd chances. Why has cheating become so acceptable? It makes me a little sad because from my own experience, from stories on here, and stories of close women I know it seems like faithfulness is almost impossible nowadays. I personally feel like a lot of people have the mentality or use the "mistake" excuse. However, cheating is a choice. A mistake is something that accidentally happens. It seems to become or be

labeled a mistake only when shit hits the fan. When an std is passed, when someone ends up pregnant, or when someone finds out and is absolutely crushed. And, no this is not me saying Every man cheats.