Bring gels or mix some sports drink in your bottles.

I used to ride with a faster, hillier group than I was really strong enough for. (I'd probably still be riding with them, but they no longer have a ride that starts near me.)

If you can tolerate a bit of frustration, you definitely get stronger. If getting dropped just makes you mad at them and at yourself, skip it. But one thing that took me a whole season to learn is that I needed nutrition on those harder rides. Because when I ran out, it didn't feel like hungry, it felt like TIRED and used up, and I thought I was just weak.