I havent read it all, but i would say this, if your in your A2 year, it happens! Seriously, its like as soon as you move into upper sixth you stop caring, its most odd. It seems like you're upset about it, which believe it or not is a good thing, because it means you want to change the way things are, and you can! Did your exams not go as well as pleased last year? Are you working harder to overcompensate maybe? I know what its like to have distant friends, I used to live in the middle of nowhwere and some of good friends were over an hour away!
My advice would be to sit down and try and think about what it is you want to change, and if it seems like everything, then choose a specific thing you want to work on. And then just write down a timetable of when you're gonna do things. like, Monday,5 o'clock Geography (15 min break at end) , 6 o'clock English (15 min break at end), 7 o'clock History, 7:45 bath/shower etc etc. And make sure you have time off. Whats between you and your friend on the tube? maybe you could meet in the middle somewhere and go for coffee or a film or something? Its all about comprimise. or you could do one week at hers, one week at yours, one week somewhere random. Its important you take that time off with your mates though, because they make you feel better about yourself.
And if you need a quick happy fix, eat a bar of chocolate! Daily serotonin is important for women, expecially depressed ones (sorry im assuming you're female). Maybe try and go for a daily run, or a swim, it works wonders. I swim personally, less strain on my body so i feel like ive achieved something after. I also go climbing on wednesdays. Maybe try and get involved in something like that.
Keep your chin up, im sure you're just stressed out! It gets like that when you're the top of the school.