I know how it feels. Now I only have three friends, one is away at university, one is always working and the other always with his girlfriend so don't see any of them really. Felt lonely before hand but now its worse.

Have to admit though helping people has made me feel much better, I haven't volunteered anywhere yet but I've helped people here and there and it made me feel happy. Like Seraphine said I'd look at stuff you could do, keep yourself occupied. For me I'm pretty sure volunteering is the best choice, hopefully you can find something that makes you feel happy too