While I do like how you have chosen to fill in the gaps, I once again feel I should point out:
Tim may think it (or not) but nowhere does Tom ever say he wants to whore his mom out to his friends. And I'm not sure where you think Tom (or Tim) has indicated that he thinks his mom is a whore.
Unless you choose the 'blackmail' route, the teacher is quite willing to carry on with Tom. She could even be the person who instigated it.
What the story has revealed so far:
Tom has been there for his mom during a time where she feels abandoned by her husband, while Tim has stayed hidden in his room. Tom and his mom's incestuous leanings didn't happen over night. It evolved slowly over months.
If you think getting drunk and making out with someone you've been flirting with for months makes you a whore, then who am I to argue? We can agree to disagree.
I do appreciate the feedback.