I really would appreciate some solid advice here, as I am somewhat at a loss on how to handle this situation. 

I am in a serious relationship of less than one year, and recently figured out my boyfriend's teenage son (15 years old) is stealing from me as well as being inappropriate. Started out small with my clothes being gone through and little things missing. Then went to him coming in to our bedroom after we were already in bed. That escalated to on two different occasions being woke up around 2:00 a.m. to his son standing over the bed to wake his dad up to tell him good night and that he loved him.

In the last couple of weeks it's really escalated in terms of the things he is stealing from me. He has taken well over $300 in perfume, lotion, hair products and most recently a new hair dryer. 

My boyfriend also has a 17-year-old daughter who likes a lot of the same products I do. So initially we were thinking it was more than likely her. Until this past weekend when she was at her mother's when the larger items came up missing. So at this point all we know 100% for sure is that he took the latest round of hair products and new hair dryer. We have searched his room and the daughter's room high and low! With looked basically through the entire house and cannot find anything. Even went so far as to go through the trash cans outside and have come up with nothing.

At first my boyfriend was insisting on having "proof" , which for me was very insulting! There is been no one else in the house other than the four of us, one of the kids are definitely stealing. For me that's all the proof I need to at least have a conversation about it.

Along with the inappropriate walking into the bedroom and stealing, this past weekend it escalated to him trying to play little mind games to the point where he kept turning the dryer knob to finished so that my clothes wouldn't dry... three times consecutively within a couple of hours. And even came to the bathroom door when I was showering and very gently turned the bathroom knob. I'm fairly certain if he wasn't just trying to mess with me he was trying to quietly open the bathroom door and see if he could take a peek. This was the breaking point for me! 

His son also had an incident at school where there was a girl in the class that he didn't know and he didn't think she should be there. He took it upon himself to point her out in front of the whole class to the teacher and make a big scene about it. This girl has had a very hard time and had been through a lot. Due to that she had not been in class for months that's why his son did not recognize her. When we asked why he went about it in that way he said that it was just fun to watch her get in trouble. 

We are going to be setting up cameras. My boyfriend is going to be talking to the kids mother today. He doesn't feel that will go well, as we're fairly sure it will be the same reaction as he did it first.. denial.

His son shows absolutely no animosity towards me whatsoever! Smiles acts happy, as if everything is fine. No anger issues, no disrespect, no lashing out... nothing. Most of this behavior is going on behind everyone's back, which is for me is almost more disturbing. 

I have always been a very straightforward person and parent. I've had no issues calling my children or a grandchildren out on their BS or holding them accountable. My boyfriend is not that way. I am in a situation where I feel like I'm walking a tightrope on how to handle this because I feel like it could definitely end our relationship. Any logical advice will be very much appreciated.

Thank you.