I think you should what makes you happy, &, what works for you! Who says we have to finish everything we start! At our ages now, it's more important to stay busy & happy. So, if that means more than one project at once, so be it. Maybe you can work out something with yourself, start something new, but in between, work on the project you have going now. Give yourself something to look forward to! Find your own happy medium...
Oh, & about books, I use to make myself read any book I started, good or garbage. Now, I read a few chapters & if it doesn't get any better, it goes in the used bookstore pile to trade in! Life is too short, & who cares if you finish every book you start!.... Some just aren't worth it!...