Why is there so much cheating in this show?

So I’ve been watching Dexter for a bit now and just finished season 4. And I’ve noticed that there seems to be a lot of cheating in the show. For some reason they always find a way to make someone cheat on their partner and it’s getting a bit repetitive for me. I just want to know if there’s a reason why there’s a lot of cheating or if they just add it because why not