What a horrible, horrible shock. How awful for you to come home to that.
I was the same age as your DD when our dad got found out. It was a horrible horrible time for us all. For a while it hurt like hell. For a while my mum went off the rails a little, but I was able to take the reins for her for a little while, making sure she ate etc, taking turns with my sister to stay in so she wasn't alone every weekend etc.
Is there anything particularly you'd like advice on?
So far what is your DH saying about mortgage, house bills etc? Do you have that agreed yet?
Can you suggest he agrees to pay all these for the foreseeable future? Until you are both in the correct frame of mind to discuss everything else.?
It was all many many years ago now of course, and both of my parents have remarried. Of course I don't particularly like either of the add-ons, but it's their life.
You and your DD will get through this. I was never particularly close to my mum before my dad left, but him leaving has meant that we really got to know one another over the years, and I now see her out of choice almost everyday. There are silver linings to everything, even if it will be a while before you can see them.
Hang on in there, it will get better and you will survive this. It'll make you stronger.
Thinking of you, you are not alone, keep posting and we'll all be here for you.