Tarzan went through puberty around apes. He was conditioned to a certain way of life because of his environment.
You cannot convince me otherwise that Tarzan didn’t get aroused by either an ape or something else and then that ape smelling that hormonal change. That ape would’ve acted on instinct and since Tarzan was raised around them it’s extremely likely that he’d follow their lead. The first time he got horny he probably didn’t know what to do. It would only makes sense that he learned how to deal with those sexual urges the same way the apes did.
As for the STD… apes and humans having sex is a big no no. The sanitation is just not there. The bacteria would be raging all around his dick. He probably wouldn’t even clean it afterwards. Gorilla parts and man parts just don’t mix. Bestiality 101