Well, all of this is speculation but...
I dont think is impossible neither. I seriously think there is a high chance Bella has some mental problems. Bella seems to think at some point that his husband is alive. I dont see any reason why his husband could be 3 years away from home without doing even a little visit.
However the problem of all this theories and speculation is that they always asume the story is perfectely logic, and a lot of times that's not the chase. I didnt thought Chad was gay, couse for me it's impossible that a girl like Sage could be in a relationship for more than a year without sex. He could be bisexual but thats not the feeling i get from the story right now. We will see.
Going back to Bella: what you say about Jill could certanely be truth. I think it was just a kiss and James was already gone, but could be the other way as you say.
I gues the cock wants what the cock wants.
Yes those are just speculations, but there are also facts.
The fact that Jill and Bella had some love story, the dialogue in the bed shows that they did something and Bella regretted it.
The fact that Bella and James did separate the moment Jill arrived in the college.
The fact that Bella feels really guilty about that separation with James, she did something that made him go away.
There are no other clues to explain why James quit Bella.
That closed room is probably James's study, it's just beside Bella's study, so it would be logic.
About Sage, the fact that she dated Chad just demonstrate that she is certainly interested in big men with muscles, i guess it's her kink. Unfortunately Chad was not really interested and never gave her what she desperately wanted, a big man with a big dick who will rock her world!!
Of course we tend to put much more in thoses stories that DPC probably imagined.
This is also the great advantage of BAD, the fact that it lets people imagine so much fun/strange/crazy stories.
We have already seen many inconsitancies, errors or strange vision of a college life. It just shows that DPC has his own logic that he uses to take shortcuts and avoid long explanations sometimes.
I don't know if he has a clear and very precise idea of that game story or if he just takes opportunities or ideas that show up.