do I wait, or do I complete the sentence?

do I wait, or do I complete the sentence? Alright, this is going to be a bit long because I really want to understand and make this new guest I have comfortable. I’m a bartender. I recently had this younger (21 in the last 3 months) guy start sitting at my bar who has a stutter, I don’t mind it at all and I just let him order and wait while he works the words out. I never really thought about it deeply, I just always listened while he worked through it. He comes in for lunch so it’s a really chill time of the day and we usually get to talking about what he’s going to school for and about our mutual interests like video games and music. His stutter is more pronounced when he is ordering something, and it’s very subtle in casual conversation. I don’t know if it’s reading thing, or something else and it doesn’t really matter what the cause is, I just really enjoy him as a guest and as a person to chat with. Today he seemed to be having a harder time than usual ordering his meal and he took a really long pause and seemed really down when he couldn’t finish the order, but he was pointing at what he wanted. I just cheerfully said ‘southwest salad today?’ And he smiled and said ‘YES!’ And he kind of chuckled. He seemed totally fine after and we had our normal chat and he didn’t stutter through almost any of the subsequent talking. But, the interaction made me think about whether I handled it the right way. I’ve never finished his words for him before and I just wanted an opinion on it. Is it bad to acknowledge what someone is trying to say if they can’t get it out, or should I just wait longer? Is there a point where it is too long and I should acknowledge or should I just always wait? He seemed more social after the interaction, so I feel I didn’t overstep today, but how can I make him feel comfortable to speak and take his time when ordering in the future? Is it situational, or should I always wait or always acknowledge understanding when he can’t finish? If anyone can give me some insight I would so much appreciate it. Edit: thank you so much for everyone’s personal stories and helping me understand. My guest (I don’t want that to sound impersonal, I just don’t want to give out his name) has come back in the last couple days and we became online friends playing Smash Bros together. Everything you have told me has really made me feel more able to support my new friend. Thanks so much!