Ok, maybe you didn't dump your ex to be with this guy.... But it seems like your jumping to him becuz now you are unattached etc and miss being with someone..
This other guy is with someone! You have to respect that! Your timing was off.... Yes, I know it sucks big time, but you have to let it go...

He seems perfect for you now, but we usually want what we can't have at the moment.....so therefore we tend to put people on a pedestal!

So, just let him be.. If he hasn't jumped at the chance to be with you now that your single.....then chances are he never will. (Also the fact hes with someone..) So yeah, I say move on.

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Appreciate the good times and learn from the bad times....