Yes. Not in Homer, but then again Homer is very coy about anything sexual.

The earliest explicit reference to a sexual relationship is in Aeschylus, in the first half of the 400s BCE — possibly in the 480s — in his play the Myrmidons. The play as a whole is lost, but a few fragments survive in quotations. The key fragments are frs. 135, quoted by Plutarch and Athenaeus: Achilleus is lamenting over Patroclus’ dead body —
σέβας δὲ μηρῶν ἁγνὸν οὐ κατῃδέσω (or: ἅγιον οὐκ ἐπῃδέσω),
ὦ δυσχάριστε τῶν πυκνῶν φιλημάτων

You did not respect the sacred bond of our thighs!
O, ungrateful for our countless kisses!
and fr. 136, quoted in an anonymous pseudo-Lucianic piece:
μηρῶν τε τῶν σῶν ηὐσέβησ’ ὁμιλίαν
κλαίων

I honoured the intimacy of your thighs,
wailing
The bits about ‘thighs’ are references to intercrural sex. Achilleus is the active partner, and Patroclus is the … I don’t know the correct word: ‘penetrated’ doesn’t seem right when it’s not penetrative.

Fr. 138 quotes Achilleus lamenting to Antilochus, saying ‘All I had is gone’.

A century later Plato’s Symposium, a dialogue on the nature of love and desire, has a character named Phaedrus discussing the relationship. The speech is largely about how love engenders self-sacrifice and noble acts. He refers to Aeschylus’ play, but reverses their roles in the relationship (Symposium 179e-180a tr. Howatson):
[Achilleus] dared to make the choice of standing up for his lover Patroclus and avenging him; thus he also died, and died for his sake. (Aeschylus actually talks nonsense when he asserts that it was Achilles who was the lover of Patroclus: Achilles was not only more beautiful than Patroclus but also more beautiful than all the rest of the heroes, and still beardless; and according to Homer he was much younger.) As a consequence the gods, out of extreme admiration, honoured Achilles to an exceptional degree for having such a high regard for his lover.
Phaedrus’ criticism of Aeschylus is based on a normative judgement that a same-sex relationship — in classical Athens — was that an older man would be the ‘lover’, and the younger partner (often adolescent) would be the ‘beloved’. That’s certainly the typical way it worked, but as normative judgements go it isn’t a very strong one, given that two other characters in the Symposium, Pausanias and Agathon, are in a lifelong sexual relationship and are both fully grown adults.

There’s a famous essay by David Halperin called ‘Heroes and their pals’ (in his book One hundred years of homosexuality) which looks at the nature of heroic relationships of the kind depicted in the Iliad, in which he casts three relationships in three ancient cultures — Achilleus-Patroclus in the Iliad, Gilgamesh-Enkidu in Gilgamesh, and David-Jonathan in 1 Samuel and 2 Samuel — as defining a special kind of assymetrical (older-younger, stronger-weaker, active-passive) homosocial relationship where the weaker partner dies, and which is simultaneously ‘friendship’ but also characterised in ways that would also be appropriate for a sexual relationship. For example Gilgamesh dreams of Enkidu as a sexually attractive woman, and after Enkidu dies he laments for him like a grieving widow.