I realise that we all have our public faces, the side we want to show, even to ourselves. Sometimes having a brave, optimistic face can hide things we need to deal with from people who can help.
But in general, there is some truth in the "fake it till you make it" idea. If we act happy and confident, we eventually become it. Dr Oz even talked about that today. I've also seen versions of that in other psychology books (with more complex explanations behind it), as well as examples on this forum.
I've even got a friend, a psychologist actually (but not a good face-reader), who thinks I'm always positive and upbeat (I always joke with her) and had no idea, until I told her, that I'd been having a hard time. But actually, every time I talk to her we make each other laugh so much that I'd rather be doing that than focussing on my misery.
So, Bewildered, you may not be always happy, and I know you've been through such a hard time, but the positive energy you show breeds more positive energy in people around you.