I have filed for a separation.
Wow, phew, thank goodness for that, you had me worried there for a minute.
His request is so incredibly disrespectful, so insulting, to you his wife and the mother of his children.
You've already had plenty of d-days with your WS, this isn't his first time on the merry-go-round, and in fact with the very same OW.
IMHO, there's a lot of steps you can pass by here. My recommendation would be to pack his stuff when he's out of the house next, put it outside and tell him to leave.
She's playing the needy damsel in distress and he's playing the KISA (knight in shinning armour)and you can't reason with that kind of crazy.
Honey he'll be full of feel-good hormones, and he probably thinks he's pretty darn awesome... there he is, saving her from....? and she "needs" him...
How long do you wait?
Not one damn minute.
He's a married man, who seems to have forgotten what that means. Married men don't get to have girlfriends. He's not trying out cars to see which one he likes best.
This is your life, your love and your self respect, don't let him dictate your future.
I know you love him, but right now he isn't the man you think he is. He's stuck in fantasy land, he's delusional if he thinks any sane person is going to wait while their partner tries out having an affair with someone else.
You will never love him back to you, but taking charge and protecting yourself could well wake him up enough to realize what his current behavior risks - loosing his, wife, family and home. That's reality.
Give him a taste of what that means if he won't leave. No chat (important kid stuff or finances only) no cooking for him, no family outings, no laundry, no errands.... he sleeps in another room... Definitely No Sex.
Have a read of the healing library, top left hand corner of the page in the box. Read about the 180 and put it into practice now, today. It's purpose is to make you stronger honey, and better able to deal with this nightmare that you find yourself in.
You might not have had any say in his affair starting, but you sure can decide how it ends. He doesn't get to have a wife and a girlfriend.
Hugs honey, lots of hugs.