Serial, while I understand that you mean having more than one partner in your lifetime isn't what you consider true monogamy, you need to understand that if you talk about being poly, people will get misconceptions.
Monogamy in human has never meant only one person in your lifetime. It's very rare among humans. Even before divorce was allowed, people remarried after the death of their spouse. People had affairs. Life long monogamy is rare and when people say "monogamy", that's not what they mean, they mean "serial monogamy". They mean "when I'm with someone, I don't see anyone else". It doesn't matter if the relationship is a few months old or lasts for years.
I think it would be bad for you to present yourself as poly. This isn't how most people understand the word. And you're not part of the minority. As a serial monogamist, you're pretty much the norm. While use a word that requires coming out, explaining stuff and possibly being ostracized while what you are is already what people assume and expect of you?
"Monogamy refers to the state of having only one mate at any one time". I can't even find a place that has a definition talking about one mate for your whole life. I mean, that means marrying the first person you date, and never dating anyone else if you break up. That means if the person dies on your first date, you never see anyone else. That means if you first fall in love as a kid with someone you could never get, you never have a partner ever.
It's very, very limiting, and therefore understandably very rare.
As far as lifelong goes, just be honest about that. Say you're looking for an exclusive but not lifelong relationship. People will understand that much better. And when describing yourself, serial monogamist will be the accepted term, not poly. And even if you think serial monogamy is a subset of poly, it would still be the more accurate and specific term.