Most Helpful Guy
Sleeping on the second date is okay. It does leave you vulnerable though if he is just have sex. I'd also be more worried about the cancelling dates than sleeping together on a second date.
Having said that it's only a new thing. Try not to get too attached and just enjoy it for what it is right now. If you want to meet up again message him and tell him how much you enjoyed that night and you should do it again. If he keeps agreeing to meet and it's been a few dates then you have the right to ask him if he is exclusive. If you go in too hot and want him to be exclauive now he may run off scared.