This sums up the relationship dynamics pretty well. And the basic personality of each character. Kida is young and fickle, Kyou is blind to anything that could complicate the simple and easy view he has on life, and Yuu repressed his feelings to point that he snapped and stopped caring about the consequences of his actions.
The gf is definitely the victim. But I assume that Kida's infidelity is the break-up moment (at the door at Yuu's place). When Kyou says he wants to speak to him properly, that's kind code "break up officially." The infidelity is the unofficial break-up point.
I don't know about you but that 3rd chapter did not even come close to being on a realistic note to me. ( • ₃ •)
Sorry you feel that way and I respect your opinion, but from talking and reading real life stories about homosexuals, I think the third story is pretty realistic. I actually talked to a guy on gayauthors.com who felt the way that Kyou does in this story.
I liked the 3rd story, it was pretty different from the previous chapters and is kind of on a more realistic note. And ok let's face the reality of the situation, the only innocent (victim) in that story is the girlfriend whom we never hear from.
Kida the cute boyfriend seems like a cheater from the start as he openly ogles other guys in front of his boyfriend and he did cheat on Kyou with Yuu.
Yuu cheats on his girlfriend (assuming he did not break up with her prior) and betrays his friend (the person he is in love with) by kissing/implied other stuff with said friends boyfriend and further goes on to finally doing H stuff with Kyou thus betraying Kida.
Kyou is also not innocent as he does not properly break up with Kida before doing H stuff with Yuu, also at the beginning whilst doing it with Kida he thinks about Yuu, the manga implies that he did not realise it but he was in love with Yuu .