I’ve told him that he can stay in the house this week but I can’t go on pretending that everything is fine. He can’t stay with me but not love me.
Absolutely this
. He's started the ball rolling, so he needs to follow through, not keep you in limbo.
I'm afraid my first thought was affair like so many others. I know you've asked him and you're sure its not that. But read back some of the threads on here and 99% of times when they're first confronted they say there's nobody else. Its all about maintaining appearances, they don't want to be the bad guy.
Please be prepared - he'll move out and within a couple of months will have 'met' his soulmate. It happened to someone in my family, Poor girl was breaking her heart wondering how things had gone so wrong and begging him to stay. He left her. Came back again for "one last try", left again and within a few weeks was living with a new woman, his absolute soulmate apparently, whom he married and had DCs with shortly afterwards.
Coincidentally someone from work he'd met a year or so before the break up but definitely hadn't done anything with. It was so obvious she'd been waiting in the wings for him to leave his wife - must have been so pissed off when he went back to her!
Many years later they still maintain the myth that it all just 'happened' after he'd blown his family apart for seemingly no reason. Men don't leave their wives with no sign of problems for no reason. There's nearly always another woman.
The rewriting of history to make his unhappiness your fault is a classic tactic too. If he hadn't wanted your DCs, he knows how they're made, he could have prevented pregnancies very easily.
Whatever the outcome, at the moment, you need space to think and you both need time to experience the loss of this marriage so that you know whether its worth fighting for. DO NOT let him get away with living his carefree single life while you facilitate it.
Too many men (my XH included) have got away with this shit, being a Disney dad while the mum slaves away doing all the childcare and continuing to take on the mental load for the family.
Make it clear that his new life will include doing his fair share of family organisation and childcare juggling. When I first split with XH I couldn't bear to be apart from the DCs but now I wish I'd insisted on a fairer split as it has hampered my employment prospects and added a complication to my new relationship, while he is free to chase the money and has all the free time he could wish for.
The new single life he's imagining needs to involve his DCs at least 2 nights a week. Try and put your business head on and get organised - come up with a schedule, work out how much maintenance he'll be paying you, make sure you're in a strong position re work and income, house stuff etc
Go to the scan on your own, or take your mum/sister for support, don't bother reminding him or telling him how it went. You can casually drop it into conversation in a week or so, to give him a taste of what it feels like, being excluded from family life.
This won't be fixed by you begging or pleading or doing the 'pick me' dance (even without another woman as competition, if the pick me dance is between being with you or being fancy free, your desperation will just push him further away.) Your best bet for either separation or reconciliation is to start to build your life away from him, show him that you're ok without him, that you won't fall apart, you'll be fine and strong and resilient (even if you don't feel that way, act like you do!).
Either it will freak him out and he'll realise what a great woman he's walking away from, or you'll start to believe it and pretty soon will be feeling the same way you're acting.
I know its hard when that's the last thing you feel like doing, but it really is the best way to make it real for both of you.