Your point could be made for almost anything. You get that new phone and swear you're gonna take care of it then 3 months later you end up throwing it around. You get a new car and you hand-wash it yourself, keep junk out of the cabin, etc and 3 months later you keep skipping over getting a carwash and an oil change. Monogamy isn't the issue. It's been said many times before but we're so used to instant gratification that we don't know how to appreciate the shit we have.
As it relates to a relationship, there has to be something that attracts you to your partner outside of looks and what they do for a living. Realistically, the way our society is set up, those are the first few things you have access. But in the first few dates, we overlook character, hide our personal esoterics, and present a person that's not true to who we are on a regular basis. We're all out to make a great first impression but in that, there's the potential to attract the wrong people for us.
That's why shit fails because after the "honeymoon" period, you look up and you realize, though you have love for that person, you don't like that mothrfckr and yall barely even share similar interests....
Edit: And another thing, stop getting into relationships if you know damn-well you don't want to be in one or don't have the bandwidth for it...be honest and just tell folks you tryna kick it