How do you know when a friend is really your friend?

My friend TJ has been my friend since i was 6. I am know 15. We have been in the same schools althrough the years up to highschool. I also been friends with Jerry and Natasha for just as long. Naturally i spent more time with Natasha (Girls tend to be friends with girls b/c boys had "cooties" and such). I had never been to TJ's house, Got his Number or really talked outside school vise versa. Cles had recently tore me and TJ apart. I had recently got to know Jerry lot more because we have the same lunch block. Now we call each other alot its great. However everytime i p TJ in the hallway i feel a surge of guilt for not talking to him. It seems silly to encourage yourself to make small talk to your friend of 9 + years. But truely, i dont nothing bout him. I never invited him or TJ to my birthday parties like i did with Natasha. Tj never talks to me much and we ride the same bus now. We rode together since we were six. So should i try to talk to him? Me and many other "Former Friends" say he's changed since Middle School. He hangs out with most of the guys. And as time progresses i dont want to not talk to him. He's not trying either. Which begs the question. Are we still friends? What makes a person your friend? When can you consider someone your friend? The years you been together, the amount you see each other, how much you know about them? Jerry insists "he's not your friend". I say "he is". I am confused. Lately, Highschool has teared at my friendships due to different/seperate cles. So much for the "best years of your life". What bull s***!