First, I want you to remember three things:
You are not a bad writer. Editing is painful for everyone. It is painful for me, it is painful for you, it is painful for every writer you’ve ever liked or admired. Despair in the face of editing is not uncommon. Don’t feel alone.
Your writing is not shit. Your drafts are a deluge of ideas and enthusiasm. They are messy, incomplete things full of your wildest potential. They are supposed to be messy. I want you to try to look at it and think ‘this may not look good right now, but it doesn’t mean I’m not good. It’s a work in progress.’
Your ideas are worth writing. You had a reason to write these things. They were important to you. They were so important that you had to write them down. They’re important enough to edit, even if it’s hard. Your ideas are important. Your ideas are worth the effort.
Now, I’m going to suggest a few different things, some of which I’ve tried, some of which I want to try. Please don’t feel discouraged if they don’t work right away.
Take a break from your work. From the sound of it, you’ve already done this. Try adjusting the length of your break. Make it shorter, when the idea still excites you.
Don’t take a break from your work. Edit as you go; stop at the end of the chapter, the scene, the day. Make little adjustments that will make you feel better when you look at it later. Tweak some dialogue. Write notes. Highlight what makes you unhappy, but can’t be fixed right now. This will make a world of difference when you come back to it.
List what bothers you when you try to edit. Make generalizations. Is your dialogue flat? Your description needs work? Take that stuff and check your favorite writing blogs or books for advice. These are all concrete issues with real solutions! You just have to find what work for you.
List what you like about your story. Super important! Don’t not do this step! Highlight awesome dialogue. Make notes of what works. You need to remind yourself that there’s a reason you wrote this to begin with.
Google that shit. Your favorite writers probably have some advice when it comes to editing. There may be a phrase or a list out there that’ll help you go go go.
Team ‘You.’ To borrow from Captain Awkward, you need to rally your support. Get your friends together, consider joining a writing group or getting a writing partner. None of this means you have to show them your work. But Team You can encourage you and act as sounding boards. Stephen King would have given up if not for his wife. People need support. Find people to cheer you on.