Mmmm the way I see it the older brother likes not shuu but his younger brother is a way that is a bit more than brotherly. Thus his stalkerishness. He was sex friends with shuu who was a substitute of his desires, and because like you said, he wanted attention. Then he finds out that the little bro and shuu are together when he listens to the audio of the bug the little bro had in his bag when the latter and shuu had their first sexual encounter. This flips a switch and he goes back to his old lover who does all kinds of terrible things to him and get him all bruised up (but like he says, its nothing compared to the pain inside). He uses his hurt state to attract the younger bros attention, and when this doesn't work he calls shuu and flirts with him, once again to attract the little bros attention (which still fails...). Then the little bro tells the big bro to stop chaining himself to him and to live his life, and the big bro (literally) tries to escape from the truth in those words.
Well that's what I got from the story, at least
ok for everyone that is confused this is what happened. shuu likes the younger brother but became sex friends with his older brother before he new that they were brothers. the older brother slept with shuu for the attention. The older brother is overprotective to the point that he is stalkerish. he bugged his little bros room and didn't want him to date shuu because of te fact that he would have a sex friend. basically the older brother wanted shuu to himself and shuuu was immature in the way that he wouldn't come out to his crush and the only one who handled everything correctly was the younger ro
ps sorry but if I put all oftheir names this would get confusing （/TДT)/ （/TДT)/ （/TДT)/