Is it normal to be creeped out?

He is a good looking man, green eyes, brown hair, nice smile his around 49 years old. (I had a crush on him before :L).
I'm 17 male, bi btw.
He is always winking at me and sometimes licks his lips.

So last week I was getting changed after my bath in my room, and he barged in and saw me naked, he smiled and left.
Last monday, we were passing each other in the hallway and he brushed his hand on my trousers where my penis was. He started to squeeze my *** a few times.

But yesterday was the worst yet. My mum was at her friends house in bedford (she was staying over). I was in my room masturbating, and I heard him approach my door, so I covered up pretending to sleep. He walked in slowly and sat in my chair (opposite my bed, the side my head was facing), I tried to peek at what he was doing and I saw he only had his boxerss on, (the ones he was wearing had no buttons on so his penis could come out easily.), I think he was masturbating, I heard fast movements and heavy breathing, but I was too scared to peak again. I think he was there for like 20-30 mins..
I'm too scared to tell my mum, as she loves him too much, she would probably believe him, (his quite smooth with her, can get her to do anything).
What should I do?.