This question was closed as a duplicate of a previous question (which apparently I also answered).
I do not believe it is a duplicate because:
- Having a boss as a mentorfigure is a different situation as the relationship will be different
- the duplicate question is about "what customs should I follow when leaving a company?"
Note that the other proposed duplicates are also about quitting a new job, not somewhere where the OP has been an employee for 3+ years and has a great working relationship with their manager.