Look at your friend's company and say "that's awesome, great for them", then move on with your life. Comparing isn't going to help if it's not used to improve yourself, and instead used as a way to meander in negativity.

Other opportunities will arise so just be on the lookout. You're around the right type of people for where you want to be so make sure you don't stop hanging out with then. As they say, you're just the average of the people you most associate with.

You could reflect on how you decided to not work with them. Do you have a clear framework or methodology that you use to guide your decision on choosing a startup? Does your framework/methodology need to be adjusted? Do you really want to go down the path? What in your eyes is true success?

I hope that helps.