Yay for B sending you a follow-up e-mail! That's so exciting- talk about a turn up for the books. That's really great news! Are you still feeling pleased by it? it sounds to me as though you've had quite a lot of good interaction recently. Have you got a plan for what next? More of good interaction to increase frequency more? or any plans to mix things up?
I love that you've been so patient and that B has been getting more open and warm with you throughout all this time.