I wann cry and scream when yuu say that he will be jealous of the guy that will love saya,...

Luckily, in their case, love leads to those lustful feelings as well. I think Oogata lost his erection the first time because most men are subconsciously trained to be "turned off" when seeing other men's penises. In grade school and high school, you'll be bullied terribly if you get an erection in the showers. That doesn't mean you don't find it appealing, it's just that you suppress it knowing the consequences of not doing so.

There are four phases to homosexuality. Recognition, realization, awakening and acceptance. Recognition happens fairly early on in life when the person notices that they are different from others, but they don't know exactly HOW or what that difference is. Realization occurs when they grasp that the "difference" they have always felt is the fact that they are attracted to the same sex. Awakening usually happens around puberty but can be delayed until as late as middle age and it involves the person understanding how their attraction to the same sex means and how it will affect their lives from here on out. Prior to awakening, most gay men will "go with the flow" and date girls, but it rarely is a comfortable or happy experience (unless they are bi). Once the awakening happens, the person has two choices, acceptance of their attraction to the same sex, wherein they will continue to have homosexual relationships or denial of their attraction, wherein they will "closet" their feelings of attraction and engage in heterosexual relationships. The latter choice rarely ends without many hurt by the deception.

In Oogata's case, he had his realization and awakening rolled into one experience. There's no explicit evidence of his recognition of homosexuality stated in the manga, but he does clearly state that he had always felt different, he just attributed it to his lack of expression. Often, when people have their moment of realization, they will admit to having always felt different but never said anything because they thought "everyone felt that way". After his moment of awakening with Saya, he panicked, lost his erection and ran. This is also common, particularly in cultures where homosexuality is severely frowned upon or criminalized. The fear of being shunned by society is powerful and can be seen in Oogata's thoughts when he thinks, "I can't." This statement has dual meanings here. He is thinking that he can't have sex with a man because it is frowned upon by society and he is also admonishing himself for not being able to get an erection with Saya. In the end, however, Oogata's feelings for Saya of both love and sexual attraction were greater than the societal pressures of ignorance and prejudice. This is made clear when Oogata beats the snot out of the guy from Saya's past who spread rumors about him. Oogata recognized his own ignorance and prejudice in the that guy's words and actions. By fighting him, Oogata was fighting himself. Once Oogata was able to accept his attraction, to Saya, "following through" with sex ceased being an obstacle.

This was truly a well written manga. There are many nuances and layers to the story that will go unnoticed if you only read it superficially. That is the mark of a great storyteller.

My apologies for writing a novel.

A really great manga, indeed.
Thank you author and translators for creating and sharing this beautiful piece.
(=・ω・=)