I don't know your feelings on speech therapy or prior experience (likely bad), but finding good therapy at this point could be a priority. As for the date, did he know you stuttered on the first date? Was he empathetic and understanding about it? I think it's very difficult to push yourself into something you really don't want to do or feel like it will be a true disaster, if not outwardly then internally. Could you let him know that you're in a difficult period with your stuttering and even though the galley sounds awesome and you'd love to join, at the moment you think something more low key would be better? He likely has no idea how much pressure and turmoil a group outing like this can cause, especially on a 2nd date where you still feel like you have to perform and make good first impressions.