Thank you so much for the replies. I will write more soon laying out more details of our marriage and how we've gotten to where we are, but I need immediate help with this particular matter today.
It's obvious (I think it is, anyway) that given H's behavior last night, I need to take some sort of stand. I am not in an open marriage, I do not condone my husband having a girlfriend, and I won't have it.
My question is, though, given our circumstances (no job, very little money, practical matters of almost certainly having to ready the house for sale, etc.), do I initiate a separation or do I handle it in some other kind of boundary? Do I ask him to leave the house, or is it enough to put him in the guest room?
Also, we have not really spoken yet today other than a tentative "good morning". My usual thing would be to be down there, follow him around knowing that something big happened that we need to discuss, and then try to discuss everything rationally.
I have done none of that. I got up early, went down to the basement and worked out for over an hour, then came directly upstairs and showered. I'm still upstairs getting dressed and have no idea what to do next.
I was going to grab some books and my iPad and just take off for a few hours, both to leave him wondering but also to keep myself from being myself at home, and to give myself some time to read, think and pray.
But at some point today we are obviously going to have to talk. And my guess is that he has come to some kind of conclusion about separating, or possibly even full-fledged divorce, I don't know. I don't know if it's a matter of he who speaks last loses or what.
I don't know what to do. I literally can't breathe. I cannot believe this is the man I've been with for 25 years.