The poet Paul Valéry said, "A poem is never finished, merely abandoned." Truer words, etc., etc.
Eventually you have to stop working on it. You have to walk away, put it on the shelf, put it in the trash, or even — horrors! — put it out there for an audience.
The Big Question is, which is it? Are you tossing it or are you shelving it? Are you giving up or are you moving on? Is it finished?
Read blog posts about ABANDONMENT here.