"but you can't tell me his feelings run all that deep, if he rather sleep with some complete stranger he met a couple days ago, instead of actually TRYING to talk with her, or even attempting for it to work.."
None of that constitutes cheating. Look, you made the claim that what he did is literally cheating, and that's what I am debating. But sure, I can discuss the other part as well
instead of actually TRYING to talk with her, or even attempting for it to work..
We do not see if he had tried conveying his feelings to her, what we do know is that Hikari at the time did not see him as a man, she described him as such to her friends, and he himself says as much about how Hikari sees him, using the exact phrasing, if the translation is to be believed. It is unlikely that he had confessed to her, but at the very least, he had tested the waters and heard back this emasculating opinion about himself, so she's made it abudantly clear to him that that's how she sees him.
Before he could attempt to shoot his shot, he wanted to make sure that he'd be standing on equal ground with her, otherwise he'd risk losing the friendship with her he treasures so much, which would be especially damning since she lives like one meter away from him so he wouldn't even be able to escape the consequences of his rejection.
"but you can't tell me his feelings run all that deep, if he rather sleep with some complete stranger he met a couple days ago
It takes extremely deep feelings for one to stay devoted to someone who they know doesn't love them back, an unhealthy amount of feelings actually. Yuu is trying to forget and move on, because, for all he knows, he stands no chance in getting together with Hikari, who's always been an existance positioned way above him.