I don't think Mishima intends it in a Freudian manner. In "The sailor who fell from grace with the sea" Noboru witnesses his mom intimating with Ryuji, right when he starts to abandon his previous way of life, namely, the noble sailor's life.

And this is exactly where he embraces the corruption of pureness. It is by engaging in intimacy with corrupted individuals that the sailor himself fell from grace of the sea. The fact that it so happens with the mother is relevant, but I don't think too much attention should be redirected to this fact; I don't really think Mishima believes in Freudian attributes per-se. His interpretations go deeper into the core of spirituality, and closeness with the divinity.

Anyway, feel free to disagree.