lost my groove

I'm afraid of this happening to me because I always seem to eventually lose interest in something, even if I love it. Or I don't exactly lose interest, I just stop doing it. For example, I love playing harmonica, but I didn't have time for it at all for the last part of school. And then once I graduated I didn't have time because I had to prepare for tests, and then I had to do applications. But now I have a tiny bit of extra time where I could play, yet I don't. I have to take apart the harmonica and clean it, and I know I really should. And I'm afraid that eventually somehow that will happen with running. But so far I've found that training for upcoming races is very motivational. Previously I was thinking I'd probably only run to get in shape and stay in shape. But then I wanted to enter a race to see where I was at. And then I ended up wanting to see better and better times. And now I want to see what distances I can do. So training for races and realizing that when I miss training days I don't improve my pace or I even lose a little, I definitely want to get out there and run. Although, once I plateau I'm not sure if I can be as easily motivated. But by then I'm thinking maybe I'd do some triathlons or something that is fun and makes me stay in shape, but not like running a specific distance where I keep hoping to set a new PR.