When there's enough emotional connection and emotional attraction built up that you feel like he's emotionally committed to you. Otherwise you'll be taking on.
There is no scientific evidence that sleeping in a bra has long-term health consequences or any impact on breast size, shape, or position on the chest.
According to Johns Hopkins pediatrician Michael Crocetti, M.D., M.P.H., teens need 9 to 9½ hours of sleep per night—that's an hour or so more than they needed.