I’m so sorry you’re going through this but I’m afraid my first thought was “cherchez la femme”
His rewriting history of he’s not been happy for years is CLASSIC cheaters script!
His not wanting to leave immediately suggests she is also married/in a committed relationship and possibly has children of her own that she doesn’t want knowing she cheated on their father...be prepared for him to do a volte face if she chickens out and he suddenly says he’s staying, willing to do counselling etc.
The FIRST thing you need to do is protect yourself financially and legally. Whatever the reason he is no longer your ally and you MUST act accordingly. Joint accounts - open a sole account with a different bank ASAP. I’ve seen so many times on here “he’d never do that to me/kids” only for “him” to do exactly that! I was a sahm with no income of my own when we split within days he’d emptied the joint current AND savings account.
“He says that he wants something different but doesn’t know what that is right now.” That sounds like long game cheaters script, I suspect he’s planning to make out he’s got himself a “bachelor pad”, ends your relationship and moves out, then within 3 months max he’ll be in a “new” relationship and will swear blind “nothing happened” until after he split from you.
Staying in the marital home (with you still cooking his meals and washing his skiddy pants?! I think not!!) is cruel and completely unreasonable, no, if he wants to split he gets lost!
“Shes not the OW. She’s a friend who also left her marriage this week” I think you’re bring incredibly naive if you believe that the timing is far too close to be coincidental!
“My ex swore on his mother's life there was nobody else.” Mine swore on dds - even if I hadn’t had other proof the baby that turned up barely 7 months after we split proved him the liar he was
“because he got angry when I asked him about his friend and whether she is the OW” you asked something perfectly reasonable in the circumstances his denial proves nothing.
I’d bet good money he’s in the bedroom deleting any incriminating texts/messages/call records/photos and pre-warning her in case you contact her husband.
Tears are not necessarily a sign of conscience but self pity and guilt as pps said. He’s crying cos shit got real! He’s no longer in a rose tinted bubble of star crossed romance
Why are YOU in the spare room? Ow or not HE is the one wants to end things, spare room for him at the very least!!
You REALLY need to find your anger and find a real life confidante, mum, sister, aunt?