Sounds like you may have found the cause of it. I’m willing to bet you and your dog were very close too. According to my mother, my stutter started when both my parents got into a giant argument of them yelling and screaming back and forth and she said I went to bed early that day and slept for like 16 hours and I woke up stuttering. I have 0 recollection of it but I believe that brought anxiety into my life, same way losing your dog did with you. And same with me, I’m fluent as can be by myself but not with others, and not because I feel nervous or scared to talk but that’s just how the anxiety manifested in myself. If it’s available to you I think therapy would be very helpful. And I don’t mean speech therapy I mean meeting with an actual therapist could help you learn to manage the grief of losing a friend in pet form and help control feelings in general and maybe you could get ahead of this and cure it or at least learn to handle it better.