Way more common than you think. There are millions of people out there that can relate. I am on of them. Been through a couple dark times and tried to end it once. Then I realized it wasn't worth it and something clicked. Things got better and I'm still here. There are a few times were it comes creeping back in but I stamp it out.
The more you're alone to be inside your head, the worse it gets. It's like mold. Starts off slow, grows, quickly grows and gets overwhelming. Need to stay vigilant with your mind. Keep it occupied with something, anything besides thinking about you and being alone.
Therapist may help, depends on you. I had a couple and one helped a lot but then it felt like she was just keeping me around and saying things I didn't agree with.
Also, a journal. Write down how you feel, get it out of your head. When you're done, close it and put it away. You will feel better. I talked to my friends a few times but I knew that if I did too much or share too much, they wouldn't hang around or would drop off. It sucks but that's how people are. Some things are taboo and sadly, this is one of them.
Be active. Can't stress this enough. Join a group or something as well that you like. Games, sports, hiking, whatever it may be. This helped me and it might help you.
Sucks as there are a lot of good people out there suffering needlessly. Also nice to know it's not just you that's fucked up - lots of people are and that's ok. So many pressures on guys these days, society as whole doesn't help that.
Be you!