Opinions on roommate issue please?

Okay so we just moved into this place me and my boyfriend, it is so nice. There was a girl who lived here before us and now we are roommates, she is a little older than us I’m 18 my boyfriends 20 and I think she’s like around 28. Anyways she has been absolutely amazing to us and so kind. Last night my boyfriend thought she was sleeping and it was like 4AM he walked out to the kitchen to get a drink in his UNDERWEAR BULGE AND EVERYTHING it wasn’t like a discreet pair of undies either they were tighht and then he commands her dog to come to him not knowing she was laying on the couch reading a book🙄🤦🏼‍♀️ he then gets in the fridge gets a water and then opens the cabinet and takes out her mio (water flavoring) to put in his water without asking! So I peek my head to see if she’s out there and we make direct eye contact she honestly gives me the worst look, like if looks could kill. I look at him and then I look at her look at the floor smile and go back to my room🤦🏼‍♀️ he is so disrespectful I am literally screaming he says nothing to her and goes back to bed. So I bought her a bunch of different kinds of Mio and wrote an apology note (are schedules are kinda crazy and we don’t see each other that often) but my boyfriend says the note is unnecessary what do u think?i feel so embarressed