Even though you built a social network for Harvard first, Facebook beat you. They out-manuevered you. I can completely see it being a huge regret, both not getting as far as Facebook and not joining them early on, but the best thing you can do for yourself is to just get over it and keep building cool stuff.

When you get old and tell your grand-children that story, don't make it one of jealousy and bitterness. Make it something that shows them the potential of small things.