The points

I'm very much into my own world. I feel so detached from other people and the external world itself that I feel I'm here mainly to watch. Doesn't make me unhappy though, but when I notice everyone behaving another way, it makes me feel kind of abnormal. Also, not sure if it's MBTI-related, but I feel like I'm not fully in a physical body. I have that dissociation/detachment thing all the time.

I take a long time to process the situation and make up my mind, but when I do, I rarely change it.

I have a lot of symbolism in my thinking, I associate images and symbols with people, and I have that thing of always writing a story that is based on the people with my life, who are put there as characters that are more or less deformed from reality depending on how I perceive it.

School-wise, I went fine until middle school and high school came 'round. I don't speak up unless I know I say the right thing (if I don't, I feel like a total idiot), I don't care much about school, and on high school, I even skipped school all the time because of depression, and because I found school really... meaningless. It felt like being overfed with knowledge with questionable basis (who knows if what we are taught is actually the real story?), and I basically started to feel like throwing up.

sound very much like dominant Ni. Can't argue against it, and I don't get why people would type you as anything other.

INFJs and INTJs can be mistaken due to having feeling/thinking functions in the middle, and I am not claiming that INTJs can never care about being socially savvy or about fitting in. But I'm just going to explain why I think you have Fe-Ti instead of Te-Fi.

Your auxiliary function is your 'tool'. You can exert it pretty much whenever you want, however you want to. It's pretty much like an on/off switch. It's kind of what you use daily, but don't really see the need of it therefore you sometimes move your focus to your tertiary function. In your case, your logic/Ti tells you that caring about people as a whole is useless, but your Fe does it anyway because it's stronger than your Ti and picks up information constantly. (I have the same thing, I'm aware of the Ni side of things yet I still use Se more because it's my auxiliary.) You becoming dependent, and detaching easily when you realize you aren't, means you can easily and casually "switch" your Fe on and off.

INFJs have both strong Fe/Fi. Means, they care a lot about other people and their feelings but they can also be very emotional themselves. This may show in you in your clinginess, emotional instability, overreactions and excessively looking for people's approval. People say dominant-tertiary loops are the unhealthy ones, but dominant-auxiliary loops can be just as hellish.

Also, this sounds like clear Fe.

I can't process my emotions if I don't put them on paper, or talk about them. I have to expose them to understand them and let them go. I have a bit of a drama queen side too, not for the "attention-whoring" thing, but more for the "blowing things out of proportion", though I usually realize I overreacted afterwards.

I could probably explain more on why I think you are an INFJ (it's one of the most easily misunderstood types), but I hope this amount of information helps.