Hi, I'm Brad, and I'm a modeling addict.
("Hi, Brad!")
Yep, you are not alone. It's easy to feed the excitement you get when you think of a subject, and buy a kit (new or otherwise), to add to the stash. And the excitement drives us to start another build. Then we lose interest, and fix on another subject.
I've tried a couple of things to deal with this. One was to make a New Year's modeling resolution. That was back in 2010, I think. First, I looked over my queue of in-progress builds, and I selected 12 of them. Then I resolved to start no new builds, nor buy any new kits (new to my stash, that is), till I had finished those twelve kits. It worked relatively well. I made it to July of that year, before I bought any kit (it was Monogram's combo boxing of their B-24D and P-40B, for ten bucks, which I couldn't pass up). As far as completing the builds went, I finished four of them that year, but I joined in some group builds, here and on other forums. While I finished those group build subjects, that meant I didn't finished more of the backlog. But I took it as a net positive that I was finishing builds.
Another thing that helped even more, was our club's annual build theme last year, which was "Shelf of Doom". At our January meeting, we each presented one or more builds that we had started but then let sit, and the goal was to finish them by the Christmas party in December. I picked 3, all 1/48 airplanes, including one of my remaining "Resolution" builds. I found that club theme helped motivate me to focus on getting those builds finished. We're running the theme again this year, but I'm trying to finish on my own.
And I don't join group builds anymore, or participate in our club's monthly theme builds. There are just too many group builds, and I find that I can't quite keep to the monthly cycle of building. I have consistently missed completing builds for the monthly themes, and when I missed the February deadline, I decided that that was it.
And above all, I remind myself that it's a hobby, so I'm not going to let it get to me, too much. I'm just working on staying focused, once I start a build, to follow through to completion.