Dad spying on another woman

Last night, I was going through one of our computers trying to find an old video that I had saved a couple of years ago. That was when I came across THE video. I opened it and it was a video of my dad placing a spy camera on a family friend's room. This friend is about 33 years old. My dad is 37. This lady moved in to our house about 4 years ago when she divorced her husband, my dad's best friend. I have seen my dad with pictures of her in his phone, accidentally. I have noticed that he looks at her in a "weird" way, and he does a lot of unnecessary favors for her. The last night I saw that video, and I don't know what to do. It has been bothering me all weekend. I know that my mom loves him, and he has been a good father, but I cannot permit this from happening. I know that if I tell my mom, she will most probably divorce him, and I would be glad, but I am not sure if I should tell her. Please help. I am 16 years old, by the way.

@SUSIEDQ: the video is just of him placing the camera or trying to hid it very well and then checking if it was placed in a good place, then him walking out of the room. He doesn't have them all over the house. I remember that 2 years ago, a little camera arrived of the mail and I told my mom, and she asked him. He said that it was his friend's camera for his dog or something like that, so I am now connecting that camera to what just happened. I saw other empty files that had the same name as the one on the video that I found, but they were empty and they are dated since like 2012, so I know he has maybe been spying on her for a couple of years. I also found another video of the girl sitting in our table just texting so I guess he was just recording her when she wasn't noticing. I have a feeling he might be obsessed with her? I also know that he watches pornography because I accidentally saw it in his phone a couple of times when I took his phone to take a quick picture, but I never said anything. However, this is way too much. Thank you so much for your respond!

You should make your mother aware. Just show her what you found. Then let your parents work it out. They'll let you know what they decide. You should not carry this burden, it's not yours to deal with. Tell your mom.