If I have read this all correctly, you are a 19 year old baptized brother that has one friend, a former school mate and now your personal trainer. You are living at home and going to Uni in Jan. You feel you have become a lying, rude, selfish and apathethic individual.
Maybe just self preservation?
Some on here have said men don't mature until they are about 25. You have got a lot to think about but are headed in the right direction.
There are always nosy Jdubs. In fact most of them have no personal boundaries. It happens in groups when you are supposed to call strangers, brother and sister.
You have approximately 10 weeks before school starts. Keep posting and venting and asking questions. Many wish we were 19 years old again with advise from the good hearted people here on JWN/JWD.
All the very best to you for a bright and happy future.