I Have a Problem

I have this problem that when I like a guy and he likes me back, in the back of my mind I'm already thinking we are going to just be friends. Maybe it's because I have almost entirely zero experience with being in relationships??? Like, I want to be in love, and I want to get married and have kids, but the idea seems so far away, if not fairytale/ mythical to me.

Do any of you have any thoughts or suggestions for me? The loneliness and this thought process has really been getting to me as of late, so I'm trying to fix it.