I can totally relate to you, on 2 levels. First, the same thing happened to me with aerobics. I loved it, participated for 6 years, and then I became an instructor. For the next 10 years I taught at various places, in 2 states. I began to hate it. I was 15 pounds underweight and obsessed with being skinny. Problem was, I was comparing myself to other instructors who were 20 years old. I went from being in my early 30's to early 40's during this time. Also, I am not a dancer and not much into music, so the technical part was WORK for me. I quit when I decided I wanted to be a consumer of the services! But, I didn't go much, got lazy and got fat.
So, my son started racing and my husband started riding. After a couple of years, my husband bought me some cycling shorts and a jersey and put me on an old mountain bike. I could barely breathe, and I thought I was in shape! My riding improved steadily; I never wanted to be competitive, but I knew I was better than the "slow" riders. I got certified as a trip leader and started leading trips for AMC and was on the bike committee. Guess what? I started resenting cycling! Then, 2 years ago, I got sick, with stuff no one has ever figured out. One of the things that resulted was I couldn't ride as fast. So, last year I did a few things to make me want to keep going.
I got a flat bar road bike I use for "smell the roses" rides, errands, destination rides, in addition to my carbon road bike. I took myself off of Bike Journal. I stopped using my HR monitor. I rarely look at my average, just miles.
Last season I rode the same amount of miles as the year before, but much slower. I also did more hiking, walking, yoga, xc country skiing, and snow shoeing. This winter, I started running. I *know* I am a slow runner, and it's just for fitness. I will never run in a race...
Guess what? In the last 2 weeks, I realized that my fitness level is back to where it was and so is my speed. But, I don't care. I mostly ride with others who are like me, or if they are faster, are not fanatic. So while most of my life revolves around cycling and other sports, it's on a healthy level. I even quit my gym membership, for the first time since I was 26 years old (I am 55), because I can do everything I need to at home or outside.
I think moderation is the key. The point is to keep doing this until you fall over and croak!