[Yoite]

Thank you all for your advice, it helps me a lot!

I agree that a year would be a really long time for her to wait, especially because I don't think she is the type to wait. Next year she will be going to university (yah, she's older) and we won't be able to see each other, maybe not even in the weekends. But even though, I don't think it will affect us that much, I'm a person who needs to have space from time to time. I think it would be the best to tell her in that period that I want to study in Japan. We see each other a lot right now and I believe she might react a bit radical (or something like that). I recall me having already said something among the lines 'I think I'll have to go to another university' and she was a bit angry and asked me 'You must be joking right?'. Ever since I didn't even dare to say 'Japan'.

I will keep all of your advice in mind when I will be finally taking the step of telling her. I think that breaking up would be really hard on her.
There’s a tricky side to it though. She has been my best friend for 2 years, supported me with high school (my first year at high school was a nightmare, especially ‘cause I didn’t speak the language) and broke up with her boyfriend for me (even though I wasn’t aware of it). So if I’d break up with her, I’m afraid it would ruin our friendship on the same time.
I’m such a mess

Well, beside that, I’ve read all the comments and I think they are all useful, so thanks! It’s so nice of you all to put time in typing down your advice and thinking of someone you don’t even know, I really appreciate it!