Today my boyfriend revealed that he had sex with his mother a few years ago for a short span of time, whilst he was 25. She would have been in her 50s at the time. This is his biological mother and she raised him. She is still with his father and they did this behind his father's back. He maintains that she's the best sex he's had and the thought of it still turns him on. He sees nothing wrong with it and they only stopped because they nearly got caught.

I am very confused and wondering what could have happened to him to cause these feelings in him. Does anyone have any experience with these situations?