Maya considers himself straight... but in another topic we consider he could be demisexual. Your right about everything. To my knowledge there is not a chapter. However in a flashback in a DJ it does show Maya looking at Nemu in the locker room changing. I am not sure where that falls in the time line but I got the impression it was before chapter 1.
http://www.mangago.zone/home/mangatopic/5111297/
The topic about Maya sexuality
http://www.mangago.zone/read-manga/imasara_briefs_no_miryoku_ni_kizukimashita/uu/imasara_briefs_no_miryoku_ni_kizukimashita-chapter-1
Spring of year two is the flashback...
The flashback is spring of year two.. volume two is when they are in third year. Volume one is in year two... but not sure where that flashback falls. But I just feel it is before and I will look in to it.
I was wondering, is there a chapter where we know why and when Maya start chasing Nemu ? He was (is ?) straight and didnt wanted to give head because of nemu's dick and he's didnt liked when nemu's friend (totally forgot his name) told him he wanted a boyfriend just like him so I was wondering why nemu ? *intense reflexion*