Welcome to the forum and I am so proud that you have reached out to get some support for you.
See that is the really messed up thing with feeling bad is that mostly people say "they don't want to be a burden". They also say that they are mostly there for everyone else and yet feel like no one is there for them. Can I ask you if you feel like your friends are a burden when they reach out to you? I am thinking the answer would be no as you would be seen as a valuable friend, as a trusted person with whom they can lean on when they need a hand up, and you are there. So I then put the question to you, why are you not worth that same love and care from them? It is hard to say "I am actually not ok", it is hard to say "I am finding things tough atm", but just as you want to care for them, give them the opportunity to care for you too. You are no burden, you are going through a tough time and you need those around you to give you a hand up, BUT..they have to know you need a hand up.
School is tough, it is so tough and there is alot of pressure and expectation put on our young people who are at the end of senior school. I am not sure why as Uni is not the be all and end all, there are so many varied pathways to careers today that even if you have not the faintest clue of what it is that might interest you as a future job you can still have options open to you. I think a chat to your school councellor to let them know you are struggling might also really help, also to see what they can put in place to take some of the pressure off you, there are some options here too.
I also wanted to mention the awesome people at Kids Helpline on 1800 55 1800, they are so amazing and it might really help just talking it out with them, also if you prefer they have a web based support service too in which I will put the link:
I hope to chat to you some more as we care so much about you. You are worth a conversation and you are worth the support and I would like to listen and to help if I can.
I think it is so fantastic you have reached out here today, and brave too.
Welcome and hugs to you