How to deal psychologicaly with being lonely?

I am usually quite happy being on my own, in fact I some times crave it. However at the moment I find my self feeling lonely, something I have very little experience in dealing with. It is almost like there is a blade in my gut, and my body temperature even feels higher than normal.

This is about a girl, curcumstance wont allow me to be with her yet. Training with my friend in his gym and talking to her are the only two things I look forwards to in my day, and today I did not get to talk to her. We usually talk a few hours online each day, and when she has to go to sleep, I feel lonely until I sleep.

What to do about the feeling now? and when we part ways each day?

If I at least get to talk to her for a while I’m ok, but today I could not, and it is twice as bad.