What am I?

It's like having the worst disease in the world
You know you have it, but cant find a cure.
It feels like the rest of your life is already decided
And you don't know if you cant take much more.
You think about it day in and day out
And then dream about it at night.
You wonder why you didn't do it differently and how its just so hard to make it right.
You try to forget about it and go on living like you're okay.
Always cautious of your surroundings and trying to decide what you should and shouldn't say.
Constantly questioning your feelings, asking "Is this real?"
You want so badly to just explain, but you can't because you're afraid of how everyone else might feel.
So you keep it bottle up, slowly letting it tear you apart.
And then go through life wondering how to cope, when someone else has your heart.