Quick, while they're not looking

So, I've just come back from an extremely rewarding four weeks at Frost Valley. I've went there for seven years there, and after the thrilling experience that was last year, I thought i had already reached my high point at Frost Valley. This summer, though, blew my mind. I met a group of diverse people, some who were irritating at times, some with troubled pasts, some I liked, some I didn't. But obviously, we were the perfect mix. At the end, we were all practically in tears that we were leaving each other. I've been home for a week and a half now. I had made goals to start serious training for XC season after one weekend of relaxation. I've run ONCE since I got back. I also vowed to do some arm exercises every day, to keep myself in some sort of shape. Well, I haven't done that. I've noticed this with myself. I have a serious tendency to excel when I have a set due date and a dire consequence if I don't achieve it. Take, for example, a big research paper I did, and presented last year. I worked harder on that than anything in my life. I probably spent every other day researching. I rehearsed the presentation for 4 hours. I edited the paper at least 10 times. And I got a 91. I did really well. With academic goals, I find it not too difficult to achieve my aspirations. Then again, I do have an IQ in the 130s. I can get a B+ in Math, Science, or History without much effort. But in a goal I set for athletics, I come up short. I have denied it for years, but I cannot anymore. I am not athletic. I am extremely lanky, I have very little muscle mass. I have small motor problems. I have low muscle tone, meaning my muscles start weaker than most people and might never get as strong as someone with high muscle tone. I have bad asthma, which affects my running. Even with all of these issues, one thing stands out more. I am not motivated. I thought I loved running. But as time passes, I find that even though my non-muscular, skinny body is actually suited pretty well for XC, I just don't have a driving passion for it. This is not the case with Ultimate Frisbee, which I picked up in the Spring. I love the warm spring air, as opposed to the bitter fall winds of XC. I love the team aspect of Ultimate. I love all of the strategy and skill. I love the TEAM, the CHEMISTRY. This is what lacks, in my opinion, in XC. the whole sport is solo, there's no fallback when you're down, no one to cheer when you're up. I don't feel that fierce connection and determination that I have for Ultimate in XC. I've tossed the idea of retiring in my head for awhile. I just don't want to let down my whole team like that, especially since we've lost a lot of runners that graduated. Speaking of them, I think that they were what brought chemistry to this team. Wilson, Kevin X, Gary, Bonnie, David, they were all such jokesters, it really helped lighten the mood. XC just isn't fun anymore. It feels like a chore, not an activity that you look forward to. I don't know what to do.