One of the main things that led me to wonder if I was demiromantic was me taking the time to really question what romantic attraction was—or at least, what it meant to me.
As far as I was aware at the time, I crushed on a lot of people in my teen years. I felt the butterflies in my stomach, I felt the urge to kiss and cuddle them, and I would generally be fixated on them for a time.
But... here's the thing. At least twice, without fully realising it, I agreed to romantic relationships with someone I never had romantic feelings for whatsoever. I was sexually attracted to one of those ex-partners, but with the other, my feelings towards them were, in retrospect, strictly platonic—nonromantic and nonsexual. I ended both of these relationships very shortly after they began because they just weren't working for me, my heart wasn't in it, and for years afterwards, long before identifying as demi, I questioned whether I genuinely romantically loved these people at all.
In contrast, I developed platonic feelings for my other former romantic partners before romantic attraction entered the picture. In two of these cases, sexual attraction had made itself apparent first, and I'd known them for a decent amount of time beforehand, long enough to develop a pretty solid idea of who they were as people.
Once I grew out of my teenage years, romantic attraction became incredibly rare for me. Between 2017 and now, I have only been truly romantically attracted to one person who is not a celebrity or fictional character: the man who is now my queerplatonic partner. Even then, the way my attraction for him developed is almost stereotypically demiro/arospec, for it took years of knowing him before romantic feelings developed, and they accompanied very strong alterous feelings as well.
Teenage me was, in retrospect, strongly negatively influenced by amatonormativity. She was clingy, codependent, and desperate to be with someone. All she ever wanted was for someone she cared about to be as crazy about her as she was about them. She didn't know, or want to accept, that romantic relationships were not her only option for close, intense, intimate relationships.
I'm still in the process of untangling my romantic history and how I really felt towards my partners and my major crushes, or "crushes," in general, but I do believe that, even if I was alloromantic in the past, there were still signs of demiromanticism. And, although I still can't quite define romantic love for myself, or what sets it apart from platonic love, knowing that love can come in so many different forms, and unlearning amatonormativity, has been massively beneficial to me.