I have very much been where you are right now & it's not nice.
My advice is take the kids & leave or if you think you can confront him without violence or a scene around the children ask him to move out.
The meth addiction will get worse. It is very unpredictable & dangerous & not something you want around your kids.
You do not have to tell your kids anything other than mum & dad are having some problems so we are separating for now.
My kids were 3 & 6 when I was where you are now & they are thriving 9 & 12 yr olds now who are raised by their mother in a healthy home.
My husband started by not coming home, he was either agitated or sleeping most of the time & I saw the porn temp files on the computer.
I didn't understand what was happening to him & stupidly went along for the ride & got addicted myself. Not what I wanted but I left with the kids & got clean. 6 years on & I have not touched the stuff, neither will I ever it again.
Believe me it will get worse & scary. Get out.