Maybe so, but Alex has only ever fallen love with Cole. Sometime denial of your sexuality is so strong that it can take you a bit to figure it out. They live in a culture where denial about this is common place. Even Alex wonders if he is really gay and not even bi. He is.
I agree on the issues part but I disagree on the orientation. Not everyone fits into the category that they automatically know who they are/who they like early on in life(Although that is true for some people). There have been many people that have learned who they are (ex. bisexual, asexual,pansexual,lgbtq ect) and what they liked later on in life and it can also change. Sexuality isn't something that is automatically set in stone,it's isn't a tight little package where everything fits neatly. Sexually can be fluid as time goes on. For example,people can suddenly like another gender/ or just a person of that gender while liking the opposite gender their entire lives. It's realistic and a very large possibility. That's just my 2 cents lol~
they're still only 21 and 22... it's pretty normal to not know everything about your sexuall orientation at that age.
I'm 23 and I've only recently figured out that I'm bi. Looking back it's obvious but a year ago I would have sworn I was hetero
I think Alex is so comfortable with himself that he doesn't over worry with sexual orientation categories... At least it looks like he doesn't care what people think of him, he is opne about who he is dating and doesn't make a big deal about it. So, when the girl was talking with him about Cole he was saying... well I may be bi or something else but that doesn't matter, I love Cole and that is all that matters. And it's not anybody's bussiness
But it seems to me because Cole is so comfortable with himself but also kind of independent, egocentric, it's hard for him to understand how to deal with Cole. He can't empathize with Cole because he has never had the same issues...
Because Alex*** (ups) is so comfortable...
but are you male or female? i'm saying this based on studies and studying it myself (for a college project and since none of my kids are completely heterosexual) that most boys know by their early teens. one of my kids is bi, the other two are pan. all of my kids knew by the time they were 13-15 years old.

at least cole knows he has issues. question is, does alex know he has a set of his own? lol this relationship is not healthy. and to be honest, guys, more so than girls(cos girls tend to do more experimenting during their teen years), know very early on what their orientation is. alex wouldn't just suddenly become gay/bi. in real life, a gay man falling in love with a straight guy always ends in disaster. but this is the yaoiverse, and it makes for a good manga lol :)