DAMN. Why do people in BL always find out that the other party is gay through shirt/coat s...

but he DID confess and senpai offered him his damn sister!!!(╯°Д °)╯╧╧

I was speaking on general terms not in specific to this.
Also I don't think he interpreted correctly and hence offered his sister or else I don't think he'd be as shocked as he was in the last page.(￣∇￣")

I agree with you about the sniffing thing. Also I must say saying I like to to someone is open to interpretation. We know he likes him but he could have meant it as I like you as a person...I mean they were talking about school and how he helped him so its understandable he took it that way. Also this manga seems like Gay for you I guess so of course his first reaction would be "oh i like you too have my sister"....

It depends on the original Japanese word/character being used in that sentence. There are different 'like's in Japanese (and chinese as well).

Yep. After reading some comments where people said he confessed I reread it and well the translation is somewhat clear on that point. But as you said the character used is important and in my experience (in manga ) they always misunderstand because of that. Usually, the person confessing needs to spell it out for the other person and I think this is a similar situation.