This is how I look at this kind of situation

In your head you build these various women up to be your perfect partner, and in many cases the fact that they're unavailable makes them even more desirable. We all want what we can't have afterall.

So, we try to move on but can't because we've spent so much time thinking about this girl that if we try to go cold turkey we can't because so many of our thoughts involve that person.

What i've come to discover is that the only way to get past these girls is to fill that space with something (or someone) else.

I'm sure plenty of you have been in relationships that have ended and you kept thinking about your ex, until you met someone else, then all of a sudden they slip out of your mind.

I guess what i'm getting at is that in my opinion the best way to get over these unavailable girls is to get out there and meet some available ones. Chances are there's someone out there who ticks just as many boxes but who isn't taken