"You just need a girlfriend."
"Why don't you date more?"
"You'd be happier if you had a girl."
This is the kind of thing I hear from my co-workers at least once a week, and most people have heard it at some point in their life when they were single. It gets more annoying every time. Why do people think that being happy or unhappy has anything to do with whether or not you have a significant other? A boyfriend or girlfriend won't make a person happier about their job or change the regrets they have about their life. If anything it will create more regrets, judging by most of human history. Besides, a person can't exactly walk down to the corner shop and pick out a guy or girl to take home. Meeting people takes time, effort and whole lot of luck.
In my opinion there is nothing wrong with being alone, and being unhappy is a fact of life. I don't proselytize my views as a single person, saying "You would be happier if you would just break up/divorce/etc." For some reason, though, non-single people can't seem to extend the same courtesy.