You Both Keep It
The keeping rule is written for one person and one thing they made. Most work worth doing has two people in it: a sheet you built together, a schedule two households run on, a draft that got good because somebody argued with it.
Then they stop agreeing, and the software has to answer. The usual answer is an owner—whoever opened the account—and everybody else is a guest. Guests can be removed. So a falling-out becomes an eviction, and whoever lost the argument loses the work as well.
We think the answer is plainer and harder to live with: you both keep it. All of it, not half each. What two people made gets duplicated rather than divided, and neither copy is the other’s to take back.
That means we don’t arbitrate. Deciding whose it really was would make us a small court with no standing, ruling on somebody’s worst month with none of the facts.
It also means you cannot un-make it. What you built with somebody stays theirs afterwards. So does what you remember.