k/k: It's a rip-off from Thomson's Select Collection of Original Scottish Airs, vol 3 (1803) p 130. I agree it's more clear than most. Here he is named as Sir John Græm (Graem) in the west country.

"...ye made the healths gae round and round, / And slighted..."

seems clear to me...he offered individual toasts round the room but omitted her. This is somewhate different than the usual "You drank a health to the ladies all, / But slighted..."

She, likely 15 years old like most lovers, was insulted.