there's a confession, a proposal and a statement same as any other couple, with a single detail that makes them different from the rest, but it's not the self-defense lessons as much as plain honesty. The truth is that Sherlock IS concerned about her safety, he is worried that she might turn him down, and he has no idea why she has that effect on him, but he's grateful for it. Not because it makes him a better person or sharper at his job, but because it makes her a true companion, a partner, a mate. A consort of the mind as well as the spirit, the better half he didn't know he needed until he found her, a relationship that rings all the more romantic because it's not.
Joan and Holmes celebrate Valentine's Day by becoming Holmes and Watson.