The idea of horns, in this case, comes from the word "cuckold" see your OED: pre-15th to early 18thC everyone--except the husband--could see the horns growing out of his head (sort of like the "emperor without his clothes" story).
Much of the unicorn mythology ties into this as well. The horn and mysterious erotica is
fascinating.
"Horn" is antlers; "horn" is masculinitly; "horn" is the erection; "horn" is also the sign of
emasculation, specifically when every one but the husband sees them on the husband's head.
In this sense, it must only = horny guy (tight balls and
potentially losing his lover to another man/woman)???
I'm new to this site, and I have been told I must back up and give an example??? I'll try.