
i've never been in a relationship but this has happened to me numerous times:
If you get happy when they walk in the room, excited when they talk to you, squeal internally over every movement they make (ex. writing, going like OMG HIS PENCIL STROKES ARE SO SMOOTH AND CUTE or something)
If you always find yourself looking at them and observing their features, if you blush when they touch you and finally and most importantly:
When you accept them for who they are, and start paying attention to their strengths instead of their flaws.

Hmm, well these feelings are most likely delusions but they're fun lol. Let's see, you enjoy your time even few seconds with them... You smile all the time when he's talking hmm... well stupid shit like that, you find the person perfect even most of the people are like " wtf r u talking about the same person"
I'm talking about a situation where my friend turned to my lover ( we broke up but still a happy memory, i wish him happiness till this moment)
I don't beleive in love/crush at first sight you need to know the person a bit.
Crushes count too ^^