Sherlock just pretends that he needs John’s help for dealing with women. Reality being, he needs advice to tone down the charm. Coz due to the lethal combination of his deductive skills and his gorgeous looks, he knows what will charm a woman and how to get things done.
But he doesnt want them to get too involved or hurt, so needs John to tell him when to stop.
One bull-in-china-shop experience with Janine was enough to teach him a lesson. ( and Mary promised to kick his arse if such a thing was repeated.)