Flaccidity

Rufus still had the problem of his erectile disfunction. He was desperate to get any or all of a number of attractive women into the sack. But he was acutely aware of his shortcomings down below. Potential embarrassment! So he shied away from women students... making him more desirable to them. He was popular with the girls for not wanting them that way, apparently. Doubly attractive... wanting desperately what they couldn't have!

He half expected Mac to fix the problem, but machines tend not to have nor understand sexual desire.

It would just have to be Viagra, sourced discreetly online.