Dont listen to the others, there are ways to reduce the rate/severity in which we stuter and since speech therapy has helped him he knows this as well. It could be that he is simply too tired after so many years and would rather spend his energy on other stuff which is a fair argument but there is something you CAN do about your stutter. Just note that most people who stutter are really insecure about their stutter and would do anything just to not stutter or talk about it so i can understand why he gets defensive about it. ps; he should be able to atleast talk about it, esp if you guys are planning to get married.