I did the same thing, 3 years ago. The day I showed up on my mom's doorstep with a baby, a 2 year old, an overnight bag and 2 eyes full of tears.
I had finally had enough of having the same fight and I was finished, absolutely finished having the same damn discussion every stupid day. I couldn't handle it anymore. And although I knew I wasn't leaving him, I didn't know what I was doing. I only knew I couldn't be there anymore.
So I packed a bag with a million diapers and changes of clothes for my kids and left.
I got in the car and realized I had nowhere to go. Nobody knew anything that was going on and I didn't really want to tell anybody. Of course I wound up at my mom's house, because getting anywhere else would have taken more conscious effort and brain power I simply lacked.
So there I stood, in my doorstep moment. Ringing my mother's doorbell for the first (and only) time ever in my life. Not sure if I wanted her to be home or not. She opened the door and I fell apart on the porch. She got my bags and helped me carry in my little ones and let me cry on her shoulder for at least 20 minutes before I offered any kind of explanation.She invited my in all of my mess into her home and held me in my pain.
I think that's what the big deal about the doorstep is. You stand there, waiting. Hoping that the person on the other side of that door will open the door and accept you in all of your mess. But until they do, you just wait. You just stand there waiting for their open arms to pull you in and take care of you.