Glad you are honest about yourself. You took the first step in recognizing the problem and now you can pin-point what to work on. Many of us, myself included, started off as AFCs. Hell, I was an AFC all of high school, through college, and well into my 30s. The venusian arts didn't exist back then. So yea, you got time to grow.
The reason why you lose interest in a girl is because of low confidence and self esteem. Losing interest and feeling indifferent is actually a coping mechanism. The other coping mechnanism is a guy who is overconfident at the expense of other people (because he is compensating for a lack of). You feel you need to get laid because it's a form of self-validation. Your cup is not full. A man with a full cup doesn't need attention or validation. When you are flowing with abundance and is confident, you are not going to be affected by things outside of you or care what other people think.
As for how you dress, who cares about what other people think? Dress in a way that makes you feel good and in good taste. Don't assume you know what other people think. Who cares. Everyone has their own insecurities to worry about even the most prettiest girl in school. As for the people who would put you down, they are the ones with the real insecurities because they feel they have to bring someone down to their own level to feel better about themselves.
I would start with any book that deals with inner game. Also another tip is never be afraid of rejection or failure.
Rejection is often taken as "you are not good enough." In the world of PUA always reframe as an incompatibility. You are an actor, but you didn't get the part at the audition because your style wasn't compatible to the director's vision.
Failure same thing. Some of the world most successful people are those who failed the most. That is where Babe Ruth got his famous quote breaking record as the player with the most homeruns, but he also had the most strikeouts. "Every strike leads me closer to the next home run"
Lastly, regarding your own insecurities, the important thing is to embrace your fears and insecurities and acknowledge them. When you embrace it, you can move past it. But if you resist it, then you only reinforce it.
That is where the basis of building a solid inner game all starts.