This is so special, this line right here. This is John’s version of Mary giving him permission to get on with his life, be the man he wants so badly to be. This is John kicking himself and saying “Just because your life has gone to shit doesn’t mean it has to be like this forever.” This is John letting go, this is him putting Mary behind him and understanding that he needs to look to his future. He needs to take the chances he thought he’d missed all those years ago because yes, “They’re gone before you know it.”, but this is Sherlock and John, they have a second chance at a life together, and by god, John Watson is not going to waste his life not saying things, he’s going to stay. He’s going to say the things he wanted to say, and Sherlock is going to do the same. That’s where all of this is going. There’s nothing left in their way, they just need to take the chance.