I’m overlooking Plutarch (Boeotia c. 46 – c. 120 AD) who lived much later than Xenophon (Athens c. 430 – c. 350 BC).
Xenophon writes in Constitution of the Lacedaimonians:
I think I ought to say something also about intimacy with boys, since this matter also has a bearing on education. In other Greek states, for instance among the Boeotians, man and boy live together, like married people; elsewhere, among the Eleians, for example, consent is won by means of favours. Some, on the other hand, entirely forbid suitors to talk with boys.
The customs instituted by Lycurgus were opposed to all of these. If someone, being himself an honest man, admired a boy’s soul and tried to make of him an ideal friend without reproach and to associate with him, he approved, and believed in the excellence of this kind of training. But if it was clear that the attraction lay in the boy’s outward beauty, he banned the connexion as an abomination; and thus he caused lovers to abstain from boys no less than parents abstain from sexual intercourse with their children and brothers and sisters with each other.
In Xenophon’s Symposium, Socrates (who was attracted to young boys though not a Spartan) is recorded by Xenophon as saying:
In contrast to this, the Lacedaemonians, who hold that if a person so much as feels a carnal concupiscence he will never come to any good end, cause the objects of their love to be so consummately brave that even when arrayed with foreigners and even when not stationed in the same line with their lovers they just as surely feel ashamed to desert their comrades.
This sounds like strong, nonsexual friendship.
Aristotle writes in Book 2 of Politics:
So that the inevitable result is that in a state thus constituted wealth is held in honor, especially if it is the case that the people are under the sway of their women, as most of the military and warlike races are,
For it appears that the original teller of the legend had good reason for uniting Ares with Aphrodite, for all men of martial spirit appear to be attracted to the companionship either of male associates or of women. Hence this characteristic existed among the Spartans, and in the time of their empire many things were controlled by the women;
Though an Athenian, Xenophon fought under the Spartan king and sent his two sons to be educated by Sparta.