emotional responsibility

We had another rough morning with me finally bursting into tears and yelling at my kids.  They huddled on the edge of the stairs together watching me freak out, Lily's arm snaking slowly and carefully around her sister, her leaning into Lily's  body in response. 

It kills me.  It kills me to think that Lily needed to protect her sister from her mother.  It kills me that I sometimes (too frequently) lose my shit and scare my children.  It kills me that it works and they leave me alone for a while after I finally let go and let them have run of my emotions.

Later when I was putting the girls down for naps I got Anya asleep and then went to sit on the edge of the bed Lily had chosen for nap that day.  I stroked her curls and whispered, "I don't like it when I yell.  It makes my heart hurt."
"It hurts you?"
"Yes."  I put her hand over my heart, "Here."
You could see her trying to work out the hurt, trying to understand what that meant.  "Like an owie?" She finally asked.
"Yes, but an emotional one.  You know how when you get really upset and you yell and cry and throw yourself on the ground.  You know how that kinda feels yuckie inside?"  She shook her head no.  Understanding emotions can be hard.  "Well when I get mad and yell, I feel badly inside.  It feels like a hurt.  The good news is that it's a kind of hurt that can be fixed really easily."
"Yep.  When you smile [she smiles] or giggle [she starts to giggle] everything is better."  She burst into deep laughter here, her face lighting up the room.  I couldn't help but giggle right along with her.  "But you know, kid.  It's not your job to make me feel better.  Remember that.  OK?  It's my job to be happy for myself."
"OK, Mom." I got up to leave and she called me back.  "Look." She showed off another cheesy grin and then giggled some more. 

I thought my face might break in two, I smiled so big. 

I know it's my job to find peace within myself, but I swear, that kids smile and laughter could change the world.  I just don't want her to feel like she has to do it for me.  

How do you keep yourself from losing your cool with your kids?