One of the worst mistakes you can make as a writer is doing the final edit on your own work. Frankly, you're too close to the material. You've slogged away over your precious sentences for hours, days, weeks, months and ‐‐ you poor soul ‐‐ even years. Not only have you formed an attachment to every word, you're also bound to see what you expect (or want) to see.
A certain level of stupidity sets in after prolonged periods of writing. Just as we're feeling our most brilliant, turns out our brains are quietly failing us. I'm not talking about a misplaced comma or a misused semi‐colon here. I mean total logic breakdown. You could sail the Queen Mary into any one of those plot holes, but you're pushing the engines to full throttle ‐‐ kind of like a bad scene from Speed 2 (as if there's any other kind).
Bite the bullet, swallow your pride -- just don't choke on the bullet) -- and admit you need help. If you don't already have a writing partner, find one. You're probably on a few mailing lists for writers. Post a request to one or more lists and choose the best fit from those who respond. The key is to share your raw work with another writer whose opinion and editing skill you trust. Should they happen to feel the same way about you then you might be on to a good thing.