I am so lonely, what are some activities, hobbies and groups a man can join to make more friends?

I would say sports or go to clubs or parties on the weekends. (This way you won't seem gay). Once you meet people it will be easier to meet more and more people.

Line dancing in your city "Park and Recreation Dept." Also any kind of hobby like painting lessons or Choir. Loneliness is bad but when we do things for others our loneliness would not seem to take an important role. See if you can volunteer at a soup kitchen. We do that all the time not just on Christmas. Seasons like Christmas makes it seem more pronounce. We do not celebrate Christmas and the stress it brings has disappeared.

I suggest you enrolling in college and taking a couple classes, like guitar, piano or arts.

Or explore a new language by taking classes or maybe cooking classes?

AA meetings/other rehab related events