Another thing that I thought of, is that this relationship is soured so even if you come up with an equitable split you still have the future to contend with. I

Another thing that I thought of, is that this relationship is soured so even if you come up with an equitable split you still have the future to contend with. In this situation what I would do personally is take the 40% on the condition that a. I am a silent partner and b. The software ownership remains in my name. I would sign an agreement that says that I cannot use or license to software so long as the (his) company. Is actively in business with no laps in between actively doing business. In the case that he stops doing business you are free to use our license your software how you see fit. This gives you two things, equity for the work you have done with no commitment to work with him further. If he succeeds then it is all good, make sure you have a forced buyout clause, where you can demand that your share be bought out or that you can sell it. If he fails ownership of the software reverts back to you and then you can have a go at it. The way I see it, that gives you two shots at making it work. Either he succeeds and you get a profit for the work you have done with no further involvement. Or he fails, you get 100% ownership and you get to have a go. Either way, it gets you out of this mess with no involvement with him anymore.