Oy. What a predicament. How good is this friend? Best friends from years and years ago, or just somebody you enjoy hanging out with? At the very least, your husband should be reimbursed his time if the friend is going to make money off it. Did you mention anything about this to his wife? Sometimes if the wife knows her husband is doing something wrong, she might "set it right"

If the friend is going to stab him in the back, why can't your husband beat him to the punch and market the prodcut himself? It would kill the friendship, so I'd only do it if they were friendly acquaintences.