This is going to sound super weird, but back when I felt that way, I went to see a psychiatrist, and he got me on meds for depression.
The meds did little except give me an excuse to act as if I should move forward. And move forward I did. I started exercising, stopped smoking, got my degree sorted out (finally). But that is beside the point.
I discovered occultism. And this is where it gets weird. It's not that occultism is the key to anything, but that it was the thing that really made my heart sing, and I didn't know it until then.
My point is that there was something out there that made my life worth living, and I didn't know it. You have the privilege of knowing what that thing is.
>the obvious solution is to just quit
No, that's not the obvious solution. Where did you get that idea? The obvious thing to do, if piano is what makes your heart sing, is to pursue it no matter what. If you have found that thing your soul yearned for all your life, you should have no qualms about pursuing it. If you don't feel this invincible motivation, the situation might be more complicated.

Now, if there are underlying issues that are making you feel this way, the first step is seeking therapy. Even if it might end up being useless on its own, just having the very intention of trying to fix your situation already puts you in a better position than you are now, and will lead you where you need to be. So MOVE.

If you kill yourself, you are going to achieve nothing, by the way. You'll find yourself very confused and will feel like a moron after you realize you go on, and your problems do too. So face them.
A side effect of being cursed to exist forever is that sooner or later, you're going to overcome everything.