i think this is actually a bit common, or more common than you think and it happens to girls too lol
I think you might be looking at ur crush through a rose-tinted glass, I dont think you can say your in love with her because if you haven't seen her for a few years then I think this is just an infatuation, you see her sort of like shes the perfect person for you, ignoring her flaws and so you cant stop thinking of the
version you created of her in your head, not in a rude way, a lot of people do this,
now you must have really liked her when you were younger but if you haven't seen her in so long and dont talk to her now, how do you know you actually like
her?
maybe you actually just like the
feeling she gave you and maybe you miss that, you said she gives you butterflies, so maybe you are missing that and not actually her,
keep yourself busy without her, make sure you are doing things or else your mind will wander and think of her, I'm trying not to take such a psychological approach to this but maybe you conditioned your memories of her to be associated with feeling happy or when you are bored thinking of her think of her, so you need to break this cycle
It sounds like you like how she looks but it also sounds like you have quite a "surface-level" relationship as you said your personalities dont really mesh, if you wanna take another route you could just try and humanize her by noticing the things you dont like about her so you can reach a point where you can identify why you two arent together and remind yourself of these when you start thinking of her,
id say keep busy,
spend time with friends,
meet lots of new people and maybe
expose yourself to new experiences e.g. talk to some other girls if you feel like it, i think its easier to see it as just conditioned feelings than this girl, you just liked how she made you feel and you miss that and maybe you didn't miss your girlfriend that much because if you two broke up there is probably some sour memories and this is maybe why you forgot about her because you saw the bad things in those memories??
also, butterflies never last in relationships, they make you feel excited but they dont last when you are actually in the relationship, so dating her wont make you feel like that everyday
i hope this helps, im no expert but i know this is sooooo annoying but its not uncommon!!