On a somewhat joking, yet somewhat serious note, maybe you should address your ADHD. You say you "tend to dive really deep into hobbies and then rebound." If you already know that about yourself, why not anticipate it and/or focus on that first so that this doesn't happen again in the future.
Do you *really* want to get into photography or not? If so, pick a system and stick with it. No one cares if you pick a Canon or a Nikon. Both can get you great photos. Flip-flopping by folks doing this as a hobby means either 1) you have too much money and you can frivolously spend it, or 2) you're too much of a gear head, more about the gear, and not about the photo taking.
If the 7D's too far out of reach financially, then wait another 6-12 months. Though the price of a new unit will never come down that much. But if you absolutely need/want a camera, then go ahead and buy it. I had a 40D before. And although I "liked" it, the moment I had it in my hands, I felt I'd eventually "upgrade" to something else (and that's before the 50D was announced).
With the 7D, I didn't get that same feeling. I am thoroughly impressed with this camera and its features. This camera feels like a keeper to *me*. So it was worth every penny of the full price I paid.
Canon or Nikon. Whatever you decide, commit to it and take photos instead of worrying about your gear. But if you suddenly become super wealthy, then buy both to satisfy the gear head in you and you won't ever need to worry.