Hi Allison,
I've been doing Air bnb for over 3 years and never had locks on the bedrooms doors, in fact my cat wants to get in and out so I leave the door ajar. Most of my guests do the same with the guest room door, on the basis of trust. This is the first time a guest has intruded into my bedroom.
All of my guests have been trustworthy and the majority are lovely people.
I would have cancelled the rest of the booking but was told by Air bnb after cancelling once before for innapropriate comments by a guest who hadn't arrived yet, that they would not waive the cancellation penalty again in future. I had words with the guest who apologised but didn't seem to think he'd done anything wrong! Because he'd apologised and I made it clear that my room was out of bounds to him under any circumstances, and that my boyfriend would be coming to stay thereafter, we resolved it enough for him to continue his stay for another 5 nights.
I've no idea what he wanted but am guessing that it wasn't to ask me if I wanted a cup of tea! He woke me up, so I've no idea how long he'd been there.