I'm fairly certain, positive in fact, that it's not good when you can't tell your best friends why you're sad.
Or even that you're sad at all.
They can't help you if they have no inclination that something in your life is making you break down.
You act happy; you listen; you help solve their problems.
But not once do you let them help you.
Keep it to yourself, hope it goes away.
I'm the best friend that lets no one in.
That's the worst kind.