No, that's not how you work it out Amicus.
house is worth £220,00 but there's still 57,000 left to pay on the mortgage. So the £80,000 is £220,000-£57,000 then split the £160,000
No! The house is a marital asset and every judge will consider where all assets go based on need alone, not who put what into it. A judge won't take that into consideration where there are kids. It all became a mutual pot when you got married.
So, the house is worth £220,000 and there is 57,000 left to pay. When the last is paid there will be a whole house of £220,000. 50:50 is £110,000
If he wants to buy you out he pays half the market value and keeps the asset, which he will eventually realise 100% of the value.
Or you sell it and then, as you outlined, split the profit.
But he doesn't get to decide that if you don't really want it.
Get to a solicitor and get it all worked out properly. No texts or emails with the words 'yes' or 'OK' in them, either!
Good luck.