from a stutterer's perspective someone telling them that their stutter is cute/sexy/cool/nice will probably make that person feel confused (how can someone like something that's bad to them?), anger (why would someone like something that's bad to them?) or maybe even sadness (reminding them of it can make them remember past experiences that... didn't go quite well). There are a million other things that person could feel (both positive and negative) but i feel like those are the most common responses to someone saying "stutters are cute/sexy/nice..." but still, that doesn't mean that's what your partner feels, and even if that's what he's feeling, there are many ways to be angry, sad or confused, so my biggest advice is to just talk to him and ask him about how he feels about it, he's the only one who can know and can tell you what you could do for him, and if he doesn't yet ask him to do some introspection, communication is always key. Hope i helped you (at least a little bit), have a nice day/night/evening!