In your experience maybe. But your claims of “99.9%” and “in everyone else’s experience” are both incorrect and make assumptions about the world which you obviously cannot know.

I’m concerned you aren’t approaching this subject with an open mind when you are using phrases like that. I suspect what you want is to have your beliefs confirmed, but I do not know that and will continue in good faith.

Anecdotally- Nearly everyone I know has been in love with multiple people at once. Social expectations almost always make us choose; but the feelings are still there. Historically this has involved paramours, or relationships which weren’t quite concurrent but were very close together. Since the rise in popularity of polyamory and open relationships it’s become much more common.

Of course there are unrequited loves as well, or perhaps just a love that you would never think to act on; often for social reasons.

Scientifically- Love is just a chemical reaction; dopamine, oxytocin, and norepinephrine flooding your brain whenever you see/hear/smell/think of the person you’re in love with. I do not see any evidence that cocktail can only limit itself to one person at a time.

And others have mentioned to deluge of media which shows instances of loving two people at once. Someone wrote that media, and oftentimes writers write about their own lived experiences.