I think it's great that you branched out and tried to ride with the faster group, and I definitely think you should keep trying. I bet you'll find that you'll keep up longer each time and, in any event, it sounds like you got dropped because of factors our of your control anyway. That said, I know how demoralizing it can be to be left behind, having been there myself. Recently.
I'd tell you to not beat yourself up, but that's easier said than done. When I'm with a friend who's beating herself up I always say, "hey, that's my friend you're talking about." So, try to be as encouraging to yourself as you would be to your best friend. And you go girl!
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher