If anyone has any links to meta or sources about m/m-fic-and-art before Star Trek, I would really, really love you if you shared them.

How about Plato's Symposium, written 360 B.C.E.?

Very different was the reward of the true love of Achilles towards his lover Patroclus-his lover and not his love (the notion that Patroclus was the beloved one is a foolish error into which Aeschylus has fallen, for Achilles was surely the fairer of the two, fairer also than all the other heroes; and, as Homer informs us, he was still beardless, and younger far).

Translation: Aeschylus is wrong wrong wrong, because it's obvious that Achilles was uke and Patroclus was seme.

ETA: Also: David and Jonathan in the Books of Samuel.