night courses

During work, John and William were chatting:
John: William, I've been taking night courses for 5 months now and I
have an exam next week.
William: oh!
John: For example, do you know who is Graham Bell?
William: No
John: He's the inventor of the phone in 1876; if you take night courses
you would know this.
The next day, the same discussion took place:
John: Do you know who Alexander Dumas is?
William: No
John: He's the author of "The 3 Musketeers", if you take night courses,
you would know this.
The next day, once again:
John: And do you know who Jean Jacques Rousseau is?
William: No
John: He's the author of "Confessions", if you take night courses, you
would know this.
This time, William got irritated and said: And you, do you know who is
George Hunt?
John: No
William: He's the guy sleeping with your wife!! If you stop night
courses, you would know this!!