You know, I had a similar situation when I was your age and it has not fully recovered. Of course, we had way less technology that you all did, but I had a similar situation. Here's mine:
As an older sister to my 3.5 year younger (older acting) brother, I later found out that after I had left for college, where I was the "center of attention" in my family and my brother lived in the shadow beneath me, suddenly, my brother became the "center of attention" and now my folks "barrelled down" on him... That was hard for him to take. Because he was entering high school with male raging hormones, when I was entering college 1000s of miles away AND my parents always compared our activities--even to this day!
Aside from the fact that I have gotten on my folks case about doing this to us for a long time, in retrospect, I think my brother was essentially acting out when I left because 1) he basically missed me as his "big sister"; 2) we always had this sibiling rivalry thing going on; and 3) he never really knew that I was actually "walking on egg shells- in the limelight-faking it" to my people and he did not know how to do that--so for some things he would get "caught" where I learned not to say too much... I guess, he resented me for that back then... I did not show him the ropes--so to speak...
Eventually, your brother is going to have to grow out of that... It may take him awhile. He needs to have is own life separate from you with his own friends. Unfortunately, he had to emote all his issues on the internet, which is really uncool, however, you kind have got to let him do that because that is "his outlet"--say for healing (to put is gently).
All you can do is tell him you love him and you always will. Tell him he is a great brother--even if you don't think he is--just be the "bigger sister" and tell him that...
It is obvious to me that he is seeking his "big sister" approval... It is also obvious to me that he has lost his "obnoxious stupid little brother" status ... Maybe he realizes that he has to grow up and be a man in general--and I bet he is wondering what your relationship is with him as his "big sister" that always use to get the best of him when you all were younger...
And stop looking at his little journal--'cuz it will only aggravate your situation... Just let him say what he says and let him get over his "phase"...
In fact, start complementing him on his posts about you... Say "Maybe you are right, I have been tough to deal with, I have got "XYZ" going on in my life and it hurts so bad that I have not been as open to you as I use to... What do you think I should do about it?" It will probably and literally shock him to think you would come to him for advice about life...
You would be amazed how much things change when you show love to your "younger--someday older acting" brother--like mine...
