Ambra -
The holidays are just really hard for a number of reasons, and feeling alone for whatever reason is high among them. You mentioned that you had a couple of invitations that you could not accepts. Do these friends have Skype? Maybe you could arrange a session with them on the holiday. Not as good as being there, but it would let them know how deeply you valued the invitation, and give you a window into the light at the end of the tunnel. If you can get outside yourself for a bit, it would help.
I also like Christine' suggestion of doing something for yourself. As an academic, I am sure there is a book that is too expensive that you would like to have. I found Connie Willis' Blackout / All Clear books wonderful for the worst of my caregiver days. Maybe a Masterpiece Theater series of DVD's would be good. The old Caligula is wonderful, with lots of scandal and a TRULY dysfunctional set of family and compatriots. If you order today (using the OCF Amazon link) you will have them for turkey day.
Maria