I'm sorry that you're experiencing some loneliness right now. Friendships, especially male friendships, take time to mature to a point where you can openly share your fears etc. I'm fortunate that one of my closest friends came in to town to visit me last night. We stayed up until 5am talking. I shared a lot of my current fears/frustrations with him and it helped. Have you ever considered seeing a therapist? Don't knock it till you try it; it can be incredibly liberating to have someone you trust that will not judge you to talk to every week. Now that I mention this, I think I really could benefit from therapy myself. I'm sorry to hear about your girlfriend, it sounds like you made the right choice. Good luck pal!
I have spoken to a therapist in the past, junior/senior year of high school and a little my freshman year of college. I've considered going again, especially because mental health is one thing my University takes damn seriously (Free counseling, pretty much as long as you need it) And part of the sense of loss is my own fault, I realized a few years ago that I was surrounding myself with people who didn't reflect the type of person I'd like to be and I made a point to lose contact with those people, but now I have my best friend and a sea of acquaintances. People who I am pleasant with, and who owe me (or I owe) a beer, but few of any real substance.