I was with you until you said you 'really need some happiness in your life'. Don't go looking for happiness in the form of boyfriends - it won't work. If you're not happy now, he won't fix that. Don't expect to hand over the responsibility for your own happiness to someone else. I'm not sure if you want to go out with him because you genuinely like him or because you want someone to fix your unhappiness. But if you genuinely like him, ask him out - just make sure you don't depend on anyone else for your own happiness.
Edit: and just because someone asked someone out a year ago (and got rejected) doesn't mean they still want to go out with them. Most people move on when they're rejected. So just for your own sanity, don't expect a 'yes' - but ask otherwise you'll never know.