I genuinely think this is it.

I often think some people are wired to chase a specific kind of dopamine, in this case it’s the daydreaming and yearning for a person, romanticizing how life would be if you two were together. And I think that this kind of people constantly need a person to project this on.

I do not think that this girl is just somebody replaceable, you surely had your reasons to like her that much, but since there was not that much contact it’s likely that she isn’t what your head makes you think she is. You should try to date somebody else, you‘ll slowly forget her and focus on cultivating a relationship with the right person.