Not necessarily. Sometimes it means it's just become routine. It happens. My fiance and I got bored and we both admitted it so we just turned things up a little in the bedroom. Tried new things, etc. It's super common. Definitely not a reason to cheat, just a reason to communicate.
If sex gets boring then talk about it with your person. Maybe y'all can compromise and start with small kinks and work your way up. If you feel like you have to cheat to have a better sex life then just dump your person. Having the balls to tell them you're leaving because you're bored is still more respectable than cheating
If you have to cheat just tell the person its over. I've never understood the need to stay with a person if you are going to cheat. That makes you a shitty person if you get your rocks off by the act of cheating.
While I agree cheating for the excitement of cheating is highly negative it's far from the only reason people do so. Leaving someone because the sex isn't good enough or because they emotionally neglect you (a reason to find affection elsewhere) isn't always straightforward. If there are finances or children involved things can become intimidatingly complex. While cheating is not the honorable way to cope it could be interpreted as the lesser of the evils in some situations.
and here i thought it was possible to love a person and do lots and lots of things with them, repeatitive things also, and yet not contract a bad case of boredom. y'know. cuz /love/ is a thing and all.
Go slow, people.
Keep it fresh