Robin wanted to work with you, flew out to your house but found out you will not work on the system. He has been begging you to upgrade the system with modifications for over a 1.5 years and you wouldn't do it. So, with that in mind, he made a better one.
If this is the case, why not do the upgrades within the partnership (if there was indeed a partnership) or at the least give full credit for the ideas that were "borrowed'?
Hope it gets resolved to the satisfaction of all.