Let it out! I'm very much the same way. I joke that I'll never have high blood pressure due to stress because I hold nothing in. Of course the flip side of that is I probably give others high blood pressure. Scream, holler, write. hell, I got myself a punching bag!

Don't respond to the moron, he's trying to engage you in a power struggle. He wants you to respond to keep it going. Of course, like all tantrums, his behaviour will get worse before he stops (in Psychology it's called extinguishment).

I'm glad to hear you say you'll handle your grandson's questions with loving care. I was adopted by my uncle and aunt and well....what I got were nothing but secrets and lies. Not thier fault entirely, many of the secrets were even kept from them. Those secrets died with my biological father last week despite my asking him several times for answers. Answers he had and refused to give. But I digress. You've got this.