AITA for asking my(26F) boyfriend(30M) about a picture he took with his friend(46F) where he was biting her cheek with their arms around each other?

My boyfriend has this friend who he claims to be his family/sister even though they are not blood related and she is 19 years older than him. I was going through his old pen drive and found pictures of them together. All the pictures were normal pictures with nothing out of the ordinary. There was this one picture where they both had their arms around each other, my boyfriend was biting her cheek and she was looking at the camera with half closed eyes. This picture took me by surprise as I wasn’t sure if it was normal for people to behave this way unless there was something going on. This picture was taken about 3 years ago. I told him that I used his pen drive without asking him about it because I didn’t want to make a big deal out of it. I used the pen drive again the next day to upload some of my files to it and all of their pictures along with the one I mentioned were gone. I asked him about it not accusing him but he got upset and told me that I was overreacting when I just asked him. Is it normal for a guy to bite the cheek of an older woman with whom he is not romantically involved with? She has caused problems between us by fighting with him for not spending time with him and expects him to spend time with her everyday. She includes herself in all our plans and expects my BF to do things for her. I never interfere into any of this but I find this as a very odd behaviour. Im thinking maybe there was something going on before even if its not that way now. AITA to think that there is something wrong with the whole thing.