I change a lot "my ideal partner"

Hello, 20M virgin here.

I don´t know if this can be that deep or relevant in a lot of ways (since i think im now used to it) but i have a little "something" that kinda bothers me a little whenever i find a girl that i like.

A lot of the times when i come across a girl that i find really attractive, a feeling of something like obssesion appears, it is not exactly like i cant stop thinking about her all day or like if i was so desperate to be with her in those moments.

It is more like if i was putting her face on the fantasies that i already have in my mind yk? (at least if theres something really specific that i like abt her, then i create another fantasy "for us"). It bothers me since i feel like those "fantasies" could get in the way if i ever try to get to know her better.

I think ive been having those kind of fantasies (almost daily) since i was like 14 or 15, and i don´t think they are the problem necessarily but maybe theres something else that i havent consider.

Also, these days, this has happened somewhat more frequently because i feel like im getting more exposure to girls that i find pretty through my friends, whether they introduce me to them or they talk about them while i'm there.

Note: This obssesion period could last from a couple weeks to a couple months, or until I realize she has a boyfriend or I find someone I'm more attracted to.

Other Note: Ive never had a girlfriend, do you think that could have something to do with all this? What do you guys think?