In my experience, you can't ride with enough people. Riding in a big group is a ton of fun and you can learn so much more because there is a lot more knowledge in the group. If you ride with people that are slower than you, that's cool too, but you need to try to keep them in sight. Try to ride at a pace somewhere between theirs and yours. This will work if you try to ride in a higher gear and keep a slower cadence.
Nutritional supplements work.
One of the best you can get without going poor is Jogmate. It's about a dollar a tube and is taken after each ride. It is really just a protein pudding. It doesn't taste all that bad and I saw results in a week. It helps rebuild your muscles and each time it does, it adds a little.