On the one way train headed to nowhere

Well.
Here I am.
Again, having to think about myself.
And truth be told, I'm doing a horrible job.
I don't drink when I'm thirsty, even though I know I should. I haven't eaten properly in a week. I get in a few square meals, but those added together don't equal much. I stay up late and sleep late. Or I wake early. It's always too early for class, so I usually end up sitting in bed for at least an hour. Thinking about everything. Occasionally crying.
Those tears. I couldn't walk away from those tears. And his face turned down so far, a perfect picture of sadness. I have only seen one person's tears that were just as sad. I suppose my dad's tears would have looked more sad if I had had the courage to look him in the eyes that night when his deepest fears about me were confirmed.
I don't know how to make myself happy. Everyone talk about it like it should be something natural, something attainable. By no means easy, but still attainable. But I've been going this way for so long now I don't know how to stop.
The train keeps chugging and I don't get off.
I tried. I failed. Being there for someone else makes me forget that I don't know how to make myself happy.
I look around and no one else is happy. How can they expect me to be happy? They tell me what I need to do to be happy, but none of them are happy. So why isn't it working? Why should I have faith in them?
I watch my roommate sleep and automatically my maternal instincts kick in (why are those things there???).
I shut the doors to keep in quiet, I put in my headphones, I tiptoe and leave the lights off. All that matters to me is that she gets what she needs. I didn't have to think about Sara anymore.
If she ever knew, she would do like so many others. She would try to hide her needs. She would feel like she shouldn't open up to me because of how I feel, but I really didn't mind. I wanted nothing else but to take care of her. Focus on her. And it didn't hurt me. I was fine.
I was fine.
Why didn't people want me to take care of them? Because they thought I wasn't happy? I was happy. I didn't want to focus on me. I wanted to take care of THEM. That made me happy. What made me not happy was when I failed.
So why don't people just let me take care of them?