He was testing his feelings and yes it’s cheating because he slept with another guy under his back he should break up before doing it or make it clear
A very twisted way of testing someone's feelings. And if you need to do that then maybe you should re-evaluate the relationship, not take such drastic measures.
By the way, as Kyouya knew nothing of this "plan" he could have easily taken the fact that he got engage as a sign that they broke up.
A normal person would take a promise to marriage for what it is. A very serious thing, so they wouldn't expect their partner to use it "for testing".
Well, you really couldn't blame him for taking such drastic measures especially since they've been together four years and Homura hasn't done anything to guarantee his love for him. He just seemed so wishyy washy with his love for him. I think Touji was desperate and impulsive, especially after seeing Homura with the guy who was in love with him.
Also, to be fair, Touji wanted to talk to him after the engagement, who knows, he might've explained his plan to Homura, but again, Homura avoided it.
Did he sleep with someone else behind his lover's back? Yes. Did they end their relationship? No. Hearin that your s/o is with someone else, true or not, and choosin to sleep with someone else, is cheating. Even if your s/o did cheat, if you don't end the relationship, or even speak to them, and sleep wit someone else, it's cheating.
If Touji wanted to talk with him he could have easily done that. So no don't excuse him on that accord. He never wanted Homura to know about it and so he got unwanted/unforeseen consequences. Yes, Homura was never all that in in their relationship (I wouldn't call it wishy washy because it's different). But you also need to understand their context and circumstances. Both of them are heirs to the Yakuza. Born and raised in Japan. To Homura it was a doomed relationship and a marriage was bound to happen just not with each other. With a woman as expected of them. So if he regards marriage as the ending of their relationship then him finding out about the engagement was only natural giving his personality that he thought they were over. Touji knowing well how Homura is should have told him in advance.
Gonna have to go read something else to relieve me from getting pissed off from the cheating uke.