It's a cop-out.
Maybe you're a nice guy, and maybe you're single. But you're not single because you're a "nice guy". You're single for other reasons, and the longer you stay in denial about this the longer it will take to fix whatever your real problems are.
So what if nice guys finish last. It will be an everLASTing event in your lives. Girls that find nice guys boring are the same ones that get into relationships that don't last because they chase after a$$holes, cheaters, drama-kings, baby-daddies all because of looks, status, or...
I've always told my guy friends this, and I like to think it helped somewhat..
Nice guys might finish last, but at least they finish, and finish well.. Jerks never finish.. They just keep on being jerks! Don't lose heart, your girl is out there!