My son’s girlfriend

How did it come to pass that I would fuck my own child’s girlfriend. Well about 2 months ago she had commented that she liked it a little rough. So I casually said that was the best way to get it. She showed me a picture of what she was talking about on the phone. And it was an older man choking a young woman during sex. I could not stop thinking about it so I sent her a gif of an older man pulling a young girls hair while fucking her. Her reaction was to say that see you get it. Meaning I knew what she wanted. The gif exchange was an ongoing thing for about a month. Each one was worse than the last and the messages were getting detailed.