So he's just left me

[YesThatsATurdOnTheRug]

Had an affair a year ago, I wanted to try, we have kids and I love him. He was desperate to try again. Now he says he can't live a lie any longer and it's over. I just invested all my inheritance in a big extension, just finished the kids new bedrooms, they are going to be so so destroyed. Can only seem to think of practical things, numb, hot, cold, shaking, don't even know where to start. Already texted my old boss for my job back but that's highly unlikely. I'm such an idiot, we decided I'd be a SAHM so now I'm just absolutely fucked, will spend my life in a two bed semi while he jets off round the globe with the latest pretty young thing (there is another one of course). I actually cannot believe this is my life!

There are some bits of good advice here, along with unhelpful shit. I’ll throw my two penn’orth in:
First, he should leave asap. It will mess your head with him being there still.
You’re assuming the worst - you have to sell the house, you’re scraping by while he enjoys the high life? Trying assuming the opposite - he leaves with nothing. You will be entitled to maintenance, child support. You own half of the house plus whatever extra you’ve put in recently. Plus the value of half his pension. A court will put the needs of the children first. So you having to sell up is unlikely.
You know this - but right now you’re in shock and not thinking 100% straight. So see a lawyer quickly - get your free first half hour, call up old contacts who might be able to help?
You’re clearly capable and intelligent, just don’t accept his way of thinking right now, it will work out okay but you should take control, starting with him getting out.