I’ve been in monogamous relationships too. Was monogamous most of my life. They didn’t feel tiring either. I’m probably older than you if anything, and none of my relationships have ever felt tiring but one - and that was the worst one I ever had, because they were not a mentally healthy person at the time. It was not a healthy (monogamous) relationship, and that’s why I said if your relationship is feeling tiring, perhaps you should have some introspection.

I was never trying to convince you of being poly, because it’s not something you really choose as much as you are born like; you’re the one who assumed something about it and felt the need to comment on it. My only guess is that such assumption comes from your own experiences.