Who was the First?

Headcanon: Mike Stamford wasn't in season 2&3 because he will only come back in season 5 when John is in a relationship with Sherlock and talks to Mike and says "I'm thinking about marriage." And Mike responds with "You're the second to say that to me today." And John will ask "Who was the first?" And cut to Sherlock buying an engagement ring. Or A perfect proposal between boys.