I'm no psychologist, but I always fall back on "nature and nurture" to explain these sorts of things. That said, depression, anxiety, and chemical imbalances may all be playing a part, and they may all be influencing each other as well. When dealing with co-morbidity, things tend to work in unison to make everything worse. Anxiety feeds depression, depression dampens your motivation to stay healthy, and changes in health can cause chemical imbalances, which can in turn contribute to anxiety and depression, for example. While people do undergo a lot of changes in high school, I wouldn't say that high school is the specific time frame where people's confidence in the future is determined. I think some aspects may be determined in childhood, and some may even be genetic. That said, I don't think it's at all set in stone. People seem to continually develop confidence over time unless something damages it, so I disagree pretty strongly with his assumption. His position seems somewhat resigned and fatalistic. When you consider neuroplasticity, it seem unlikely that the events of a few years of high school can rule the rest of your adult life, unless you believe that it will, at which point it will no doubt become a self-fulfilling prophecy. If you're feeling self-conscious, I'd imagine there's some degree of low self-esteem and anxiety, but--again--I'm no psychologist, so it's definitely worth talking it over with a professional. If you can't get an appointment, call a mental health line or find a site to chat with someone. If you genuinely believe that girls are much more emotionally in tune than men, that they can tell in an instant that you aren't confident around them, and that a lack of confidence around them is an instant turn off, then nothing good is going to come of it. You're having trouble beating this dilemma because it isn't a dilemma at all; it's a false dilemma. Things aren't black and white. Not all women are more emotionally in tune than men. Not all women are perceptive enough to spot a lack of confidence right off the bad. Not all women are instantly turned off by a lack of confidence. There's a huge variety of personality traits, interests, and desires among both sexes, so don't trick yourself into believing that you need to be a certain type of person just to have a chance. Just look at all of the niche genres for books that are out there. Surely, if people's interests in books can be so broad, their interest in people is relatively broad as well. A variety of people write those books, after all. Now, this is just a personal piece of anecdotal evidence, but I'm not emotionally in tune, my partner knew right off the bat that I lacked confidence around her, but it wasn't an instant turn-off. In fact, she dislikes confident jackasses and favors people like me, and--judging by how much I can relate to you--people like you.
In short, fresia that dilemma; it doesn't exist. Try to make some platonic friends and be yourself around them. There are most likely people out there who can accept you for being the way you are and love you in spite of it, and if you surround yourself with people you're comfortable with, you're liable to gain confidence. If you latch on to the belief that you don't have a chance because you aren't a certain type of person, that prophecy is very likely to fulfill itself and make you feel even worse, possibly even embittering you if you hold onto that belief for a long time.