[HUNTA-800] My brother is getting married to his girlfriend of over two years. But what he doesn’t know is that I’ve been secretly having sex with her since she first came to our house a year and a half ago.

In what way?

The title is

兄貴が2年以上付き合っている彼女と結婚することに。でも実は彼女が初めて我が家に来た1年半前から、ボクが中出しし続けているのは兄貴は知らない。

It’s on the cover

Google translate translated it:

Aniki ga 2-nen ijō tsukiatte iru kanojo to kekkon suru koto ni. Demo jitsuwa kanojo ga hajimete wagaya ni kita 1 nenhanmae kara, boku ga chū dashi shi tsudzukete iru no wa aniki wa shiranai.

My Big Brother is Getting Married to His Girlfriend, Who He’s Been Dating for Over Two Years. But He Doesn’t Know That I’ve Been Creampie Fucking Her Since She First Came to Our House a Year and a Half A Year Ago.

And what plays matches the photos on the back cover