I go to concerts by myself all the time. The wife only likes some of the stuff I like to listen to and my friends either 1) don't like metal, 2) aren't willing to spend money, or 3) are total flakes. Seriously, I have this one friend from work who will say he'll meet me at a show and its 50/50 whether he actually comes. And if he does show up it's often halfway through the 2nd band of the night and then he leaves before the headliner is done - I don't get it.
Although there is a lot of standing around in silence, concerts are a great place to people watch and usually I can find a few people to talk to before the show and between bands. Moral of the story: going to concerts solo really isn't that bad.