My interests can also come and go with the wind and I can get quite obsessive as well. What I do to try to moderate myself is I set aside a little bit of time each day to continue to do whatever it is I'm neglecting. My interest in my writing, for example. Regardless of my current feelings surrounding it, I attempt to do a little bit each day. I'm always thinking of the other things as I'm doing it on those days, of course, but I feel a small sense of accomplishment knowing I did something.