If you are not currently generating any money, I would avoid adding him to the LLC. There are too many issues to deal with. Maybe you could just offer him a small amount of compensation, 3 months is not really that much time.
Also, most operating agreements have all these clauses to cover cases where he wants to sell his share to someone else. Say he sells to someone with a lot of money and big lawyers. There is a small possibility in this case that you would be spending most of your time and money in a court setting.
It is best to try to just pay him to walk away.