<human>: One of my friends at school is dating a guy who is 10 years older than her. She is 16, soon to be 17, and I am 17. Her boyfriend lives with her and her parents and he is a friend of her dad. She has told me that they have had sex and a while ago she feared that she was pregnant (thankfully she was not). To my knowledge, her parents nor anyone else in her family know of their relationship.

In spite of her alarming relationship with this guy, I want to date her. I have told her my feeling about her relationship and she agreed with my opinions. She told me that she left a note on his bed saying that she wanted to break up with him and he that he left her a note saying that he did not want to. 

I'm not sure how I should go about handling this situation. If I do end up dating her, I will fear that she might cheat on me with her ex-boyfriend considering they live in the same house. However, if I do end up dating her, I plan on speaking with her ex and telling him if he "drinks my Kool-Aid", I'll put his ass in prison.

Condense the text into a few key points
<bot>: My 16 year old friend, who I want to be my girlfriend, is dating a guy 10 years older than her.