Its tough... I know that stutterers put people they interact with in an uncomfortable position. My friends were great growing up and I wish everyone would have been like them. Essentially, it was never acknowledged. If I did stutter, they'd patiently allow me to finish and rarely (if ever) make even the slightest sign that they found it annoying or amusing. I never asked them to do this, I just feel that they cared about me and liked having me around and because of that, it was just a big nothingburger. That ultimate effect on me was when I interacted with them, my stuttering was at a minimum. I was comfortable and therefore forgetful of my impediment. So my advice is, if you like this man and want to making something of a relationship with him, treat his stutter like its a big nothingburger. Never smirk at him when it's happening, never seem impatient or frustrated. Just patiently wait as if it's not happening. There is nothing particular you can do to help besides being a patient and caring individual. I know that can be hard to do, but it is something I always appreciated.