What alternatives do you offer when he asks to nurse? If it's cuddle time and a drink that he wants, can you offer that to him instead? A book snuggled by mommy and a cup of his favorite drink? Even some kind of treat that he normally doesn't get?
Maybe the negative feelings will decrease once you get Joshua to cut back to fewer nursing sessions. And decreasing is the first step to fully weaning, so just take it one step at a time.
I wonder if looking at photos of Joshua as a baby, breathing exercises, or reading/listening to music while you nurse Joshua would help you relax. Just making some suggestions.