I've known them for 5 years and they are already in a relationship

When you ask them straight up… me and my gf decided to start dating after 4 years of knowing each other on a ski lift in the most casual way possible

Lol

That line can vary by the person you're dealing with. Some people just want to be really good friends, like me with Hannah_Wolflover4, who I do spend a lot of time with and give a lot of hugs.
But then some people might think they just want to be really good friends, and then realize that they actually really like them, like me with my crush (wow I'm such an example).
I'd suggest that you try to ask them and see what happens.

Title-
;-;

Well I read that before writing this comment

Oh-

It is possible that they're polyamorous

She isn't tho
She prefers bisexuality
She doesn't even know what poly is

Oh ok

This person might just have sensory issues (like me) and just really likes hugs. They could also just be clingy (Also like me)

Seems about right
They did tell me they are very clingy