In gambling, the "over/under" bet usually refers to some total number in a contest. (For example, total number of points scored in a football game.) That said, I'm not sure how it applies here.
Heh, one of the things I first learned in high school freshman-year Latin.
Aside, I really don't get what's so hard about "We don't know Durkon's sexuality for sure, and it's okay that we don't know. We don't have to try to figure it out." (Basing that speculation on in-comic evidence is, admittedly, better than appealing to flawed and probably-not-applicable real-world statistics. But it's also okay to let it be inconclusive!)