Audio problem: When Janis shouts at Cady out of Damian's car, Cady says "It's not my fault you're like in love with me, or something." After she says this, her mouth visibly moves saying more words, but no audio is heard. (00:58:40)
Audio problem: When the Spring Fling Queen nominations are being announced applause can be heard for both Janis and Cady but no one in the class is clapping.
Answer: Precisely because he was sleeping with a student. Getting her pregnant would bring their affair out into the open and create a scandal for the whole nation to know what he was up to. Therefore safe sex was really important to him.
The_Iceman
True, but since he was spending time with her, he could make sure that birth control was being used (i.e. him using a condom). I think he was trying to appear "uptight" about sex, so he could be the least likely suspect.