You can't just "ask" someone to lose their stutter. It's not an item on a grocery store list that you can just check off. Chances are he's fighting a mental battle with himself every day trying to reduce his stutter on his own. It's exhausting, honestly, trying to figure out what you're going to say next to avoid your hard words, mentally preparing yourself for the reactions you're gonna get from people. Having a stutter is mentally tiring and honestly, can lead to a lot of self-deprecation. The chances are high that you don't know a lot of the mental battles your fiancé is fighting because of this disorder. If he's been to therapy, he probably has his own techniques and ways of coping. However, for a lot of us especially in adulthood, if it hasn't grown out, it's something you'll be stuck with for a long time, maybe even for the rest of your life. There will be good days for fluency, and some days worse than others. Just BE there for him. Support him. Let him know that if he wants to go back to speech therapy, you'll be there for him. Either way if you really love him and want to be with him, you need to take him as he is, stutter and all. It's not just something you can snap yourself out of.