Part of finishing is committing to stick through the dull/boring bits. There are very few pursuits without those bits - it's a life skill, not just a writing or creative skill, to push oneself to persist through them, to enjoy the process or believe enough in the end result (or just plain need the end result - especially if money is involved) that one doesn't give up the moment things look sticky or bland.

As for what to do about... it's gotta come from within. Setting up schedules and deadlines and concrete goals can help, though one often needs accountability of some sort to fix a habit change. Holding an image in your mind of the end result, the feeling you'll get when it's Done, can help, too. Though part of it's just the plain "butt-in-chair" habit of Sitting Down and Doing It, even if it doesn't come out quite as shiny and perfect as you might have worked. (And it probably won't, at least not until you've worked at it for a while. As the saying goes, the way to carve an elephant from a block of marble is to chisel away everything that's not part of an elephant... but you're going to burn through a few blocks, first getting gravel, then something vaguely quadrupedal, and finally ending up with an elephant. Procrastinating on picking up the chisel in the first place isn't a shortcut to the elephant, it's keeping you from learning what you need to know to carve that elephant. Nobody's born knowing how to hold that chisel or carve that elephant, and every carved elephant you see out there - by people who make it look easy - stands on mounds of shattered marble and mistakes.)

It may also be, since you claim this problem affects the rest of your life, an issue that needs extra help. Issues like depression can seriously mess with one's ability to focus and finish, and don't go away on their own.

Good luck!