first, i'm very sorry you're going through this. mental health is tricky to navigate and individual to each person - nobody can know what's going on in your head just from looking at you, which means it can be very easy to hide. it's a little tonedeaf that some of these replies expect you to build resilience when your resources are probably at their lowest. it's a dangerous mentality that mentally ill persons should just "shape up" and it's a stigma that still lurks around today despite all the positive changes to social perceptions of mental health (read: toxic positivity regarding depression and other health issues)
a warm hello, from your friendly neighbourhood drop-out 👋 i won't go into specifics because no one wants a trauma dump, but i've been dealing with poor mental health ever i was little. when your childhood is touched by it, you don't really know any different - and the only way that i can see it for what it is now is because i'm on the other side of it and i know what happiness looks & feels like. so i understand some of the weight you're buried under but, because i'm not you, i won't ever know exactly how you feel. that's important to establish.
i got bad gcses, school refused to keep me on. went to another college for a levels where my mental health degraded further (lost my few friends and was unable to make new ones - big up high functioning autism). i ended up having another psoriasis flare-up from the stress and i was pulling out chunks of my scalp in the disabled toilet where i hid at lunch. i think i got a C in my spanish AS level and failed everything else, college refused to keep me on to finish the quals.
my issue is that i didn't know how to communicate what was happening. i didn't have the language to say all the things that were whirring around in my dead mind, and i didn't know any of it was wrong either. i figured everyone had those problems and they just got on with life better than i did.
you seem to have an understanding that what you're going through is wrong, and i can't understate how much of an advantage that gives you. you have an awareness a lot of people don't have - you need to use it. please, please speak to somebody safe about the issues you're facing. family, school, support charity/worker, anyone safe that you can get your hands on while you have this lucidity. communication is key - it's the only way we survive in this world. you have to tell people, even if they can't do anything about it. you're releasing a part of the burden that way and someone knows your mind a little better then. steps can be taken in the right direction.
as for the actual dropping out - nobody can make this decision but yourself. it's complicated. i left formal education at 16, got a crappy job and then went to work properly at 18 (where my mental health hit its lowest low because i hadn't expected to make it that far and thus had no plan post-18). i'm now 27, feeling one million percent better and happier: i've cut off the family members who made my life hell, worked on my social skills and have actual friends & found family now. i own my own business and have published some poetry, working on a stageplay. creativity is why i'm alive and being depressed, paranoid and all manners of ill suppresses that muscle, so i genuinely had nothing "good" to live for in those years of my life. losing your passion is an unforgivable trait of depression, don't let it win.
however, none of it was easy. when you leave school you depend entirely on making money to survive, which means working as much as you can. as in my case, my early jobs twisted the knife so considerably that my failures at school were just the tip of the iceberg. for me, the problem wasn't school or work, it was the world occurring inside my head which was affecting my perception of the world outside, the stage we perform on.
and that now leads me to this: personally, i'm ready to continue education but as a mature student almost a decade later wanting to get back into it with little to no qualifications... it's difficult. however, from the sounds of your situation, you again have an extremely good springboard (good grades, self awareness, a plan to return, etc). being one, two years or even fifteen years behind your peers' journeys is not what you should be worrying about. your own journey is most vital and nobody else can explore it but yourself.
i'm telling you all of this so you have something to compare to. as a kid still in school, as much as you may hate to hear it - please don't take offense - but you truly don't have enough experience from your peers to wholly understand what is waiting for you out there, so i hope this account helps you to measure yourself against something from "outside".
if any university shames itself for not considering a top student just because they had the nouse to take a break, it probably isn't a university you want to be attending anyhow. don't break yourself before you're even out the gate - a horse disappears for breaking a leg on the track.
tldr; speak to somebody safe, weigh up your options which are individual to you and nobody else, follow the plan and keep it flexible. no education is worth your life or your happiness. whichever way you choose, do it with strength and conviction. you will get there one day and i'm rooting for you 👍