Q. If I wrote a script, then invited a friend to come cowrite and fix it up, he changed everything, can I go back to my original and take it back? They were all my characters and concepts. He will not talk to me at all now. Is the script dead in the water or can I take it back? I registered it WGA after I wrote it. Then reregistered the second version with both our names on it. I do have proof the first one though was MINE. Help.
This is why people sign collaboration agreements: to make clear what you're agreeing to when you collaborate.
In the absence of a paper agreement, the question is, what did you agree to orally, or what agreement was implied, by your collaboration?
If you don't use any of his stuff, I think you're technically, legally free to use your old material. However if any of his stuff has crept into the old stuff, then you can't. (I am not a lawyer. This is not legal advice.)
Generally I would not agree to co-write with a friend unless we agreed that I was permanently attached to the project. Otherwise I stand to lose all my work if my friend changes his or her mind about my creative contributions. So I completely understand why your friend is pissed off.
Is the project really more important than the friendship? I would rather lose a project than a friend.
I would distinguish between comments and writing. If I give you notes, you're free to use them or not, and I don't gain any sort of ownership over the project. It's only when you ask me to start writing things that I would expect to be part of the project as it goes forward.