Literary Choices

I was asked to work on my novel Miraculous Boy.  My agent is asking me to do rewrites.  My agent is rare.  He won't give up on this book.  MB has been on the market on two separate occasions and hadn't sold.  Frankly, I'm tired of this book.  I've put in ten years into writing and rewriting this book.  I swear in all the time I'd put into it, I wondered about the job opportunities I didn't take up or the relationships that passed me buy.  I chose art making over everything else. 

Writing a book means that there are other aspects of my life I had to give up or did not pursue.  We are our choices and I chose to write.  This is not a bad choice.  I don't regret the creative process during the last ten years, but I'm nearing fifty.  At what point should I just give up and find other ways to grow my life?