Ultimately, you have to be honest with yourself and make the best decision for you. I don’t see how that’s for anyone else to judge. (But, of course, that’s not going to stop anyone.) I’m in a slightly older demographic category than you and I know several people who upon hitting middle age left their marriages not because there was anything wrong with their spouse, per se, but because they wanted something that they weren’t getting from their marriage. The good old mid-life crisis at work. You’re just pulling the trigger a little bit quicker than most.
If it’s called selfish, so what? It’s your damned life, and you’ve only got one to live. It does get a little more complicated when kids are involved, but even then it’s not necessary to stay together to successfully co-parent. That’s a different issue, though.
EDIT: After posting this comment, I read the following article about why you may not want to try to hold on to your marriage. It can lead you to doing things you will probably regret.
