I feel your pain! I used to be terrible about this when I was younger, and I always described it as "intense longing, but very painful". Like it actually hurt physically to not be with or near the person. I was so bad I would get obsessed with famous people as well as "real" people,
The tendency to feel this way has slackened off the older I get and it's almost gone now. But I do remember it well, and sometimes certain songs or smells remind me of a past "phase" (as I used to call them), and I will still get a twinge of sadness or longing, but it passes. Good luck! 
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DeeDee327
~having Asperger's is an advantage I think. Because I do not understand social "rules" or the "proper" way to behave, then I don't take myself too seriously!~