I'm so sorry you're hurting right now, Pre, but I'm so glad that you're coming here for support. Neither leaving or asking for help are necessarily easy things to do. Eventually, you will feel better. It takes time, though. Please remember to be gentle with yourself while that time passes.
As far as your 21st birthday... No one says you HAVE to go out and celebrate by drinking for it. I didn't, but I should also mention that for the majority of the weeks around it, I was stuck at the library or computer lab working on final projects. I did, however, manage to take a small break for an impromptu drive to the coast with friends. Campfire and s'mores at the beach.
(I have to say that any friends that did party hard for their 21st, their memories of the night were rather fuzzy. I much prefer my rather geeky but clear ones.) I hope your 21st birthday is filled with making good memories, whether it's with friends or a quiet evening.