"I don't want to be part of this family!"

I think every kid has said it--"I'm running away!" or "I don't want to be part of this family!"

Well yesterday was #4's turn to say it.

Thursday is the day of being tired, in this house. At that point, we've made it through 4 days of school and 3 days of after school activities, which makes us all tired.

Yesterday was no exception. After 3 agonizing tries, 9 +9 was still = 20, on his math homework paper....and then he lost it.  I tried to calm him down, redirect, give him a minute to settle down, and threatened. That led to getting a spanking, at which point he screams, "I don't want to be part of this family!!"several times.
My response? I told him that since he didn't want to be part of the family, he needed to remove the clothes and shoes that I bought. As he headed upstairs, I gently reminded him that our family lives upstairs, so he would need to leave. Well, he did. Walked right out the front door butt-naked. I peeked out the front window, and there he was sitting on my chair on the front porch peeing.
I opened the door and gently reminded him, that the porch and lawn belonged to our family, so only we were allowed to pee on it.
He then ran to the van. I walked around the van and found him standing there, naked and crying. I asked him, if he felt a little silly standing outside naked. He said yes. I told him that even though he didn't want to be part of our family, I would be glad to share some of our family's clothes with him, so that he didn't have to be naked anymore.
So we walked inside. I started asking him if he needed to borrow anything else, like a pillow or a blanket, or maybe some money, since he didn't have any.
He sighed really loud, frowned, and said, "nevermind. I do want to be part of this family. I'm sorry."

I still can't believe he peed on my front porch.
What's a mom to do?
:)