You're not a shit, Sherry.
You're just self-aware and honest. And that's something that "Shits" run away from. You've had a hard few weeks/months and you're feeling it. Understandable. People of our age are somehow supposed to be immuned to such things - who makes up these rules anyway? But we are.
Don't dwell on it. Your sister and nephew will understand. You love them, they know it, they love you - what's the problem? Honest communication is a balm. They'll get it.
Take care. 💚🌹