Stress, nervousness, anxiety will all cause stutter to be worse. That’s almost 100% true. Stutter does fluctuate. It will be less or more. In my son’s case he does not repeat words or sentences, he gets something called “block”. He struggles to get words out for a few seconds. Not every word but it does get worse when he is nervous. He absolutely has good and bad days. In a more comfortable environment like with his siblings and friends, he stutters less. As someone suggested that you can nicely tell him that you are aware of his stutter and comfortable talking to him. Maybe that will relax him and he won’t try hard to mask his stutter which honestly will make his stutter worse. Like this guy, my son is very good looking (not saying this because he is my son… lol but he is), very smart, high achiever and an empathetic person. If the guy you are seeing has an amazing job despite his communication struggles or struggles in general in life, his perseverance must be another level.  Hope this helps.