Horse Riding Anxiety

Today Steven and I rode in the pasture with friends. I worry constantly about how Steven is doing on Rupert and it is affecting my riding. I was so proud that as soon as I was physically able, I got back on a horse. I've done trail rides and play days but riding and practicing in the pasture makes me a basket case. I need to get back in the round pen as soon as we get ours back and then hit the arena to practice loping. Also, I've got to lose weight. I've put on a few and it also hurts my riding.