Olly,
You said that you were studying hard to get into college, than the narrative change to going to the Army. So, I really don’t know what you want to do, but that maybe because you also don’t know as well.
Let me tell you one thing I know. Popularity is something seriously over-rated. My opinion is that is better to have only one friend, or at times none, than to have bad friends that are negative company to you, and that provide you with a false sense of camaraderie where no true friendship exist. Sometimes family feels the void, or you just have to wait and try to develop friendly relationships as time goes by. Both college and the Army are great places to make friend. High school is not such a great place to make lifelong friends because we are very young and we are still changing a lot. Just like yourself.
A lot of people tell you they had their first kiss by 18 y.o and much more That does not mean it is true and that it happens to everyone. It also is an irrelevant fact. There is no set date to do any of it. It does not make you more macho or smarter or anything. The weight issue is a health issue and if you go to the Army they will make you thin or not accept you to begin with. It can be more difficult to find a girlfriend but not impossible. It does not interfere that much with friendships. It may cause problems with your self esteem though.
You seem to be a pretty nice person as it is. You decided to improve your grades and you accomplished it. I guess you can do whatever you want. You know how to write quite well, you expressed yourself without problems and gave an interesting view of your problems. You say you have insight and acknowledge positive and negative aspects of your personality. Well done.
There is time for everything in life. Socializing is only a part of it. At your age it may seem like socializing should take 90% of the time but it is not really the case. You need time to rest, to study, to work, to do many things. Socializing is only one aspect of life. Life is not only partying.
Go to college and study. Let your high school “non-friends” party-only. You don’t need them anyways. You are growing, and they are not.