Well I'm not a lawyer but I think the answer is almost certainly "no". You didn't have a business partner, you had an employer who owned the business. He clearly leaned on you heavily for the expertise to start it (you aren't clear on whether or not you were paid for that work at the time, and how, presumably by salary?) but by your own admission over the years since you've not really been involved and whatever it was the company did, it obviously managed to carry on doing it successfully without your input and didn't need your input to sell it either.
If there's any claim it would be in some way because he misled you about the set up and you believed you did part own it.