If he has any morals though, he'll sell up and give you half. So does he have any morals or not? Because it has a huge impact on your future.
It's also just dawned on me that as this situation seems new, you could still be paying half the mortgage. If he's indicated that he has no intention of selling up and giving you half the equity or if you think that's what will happen, you should definitely stop paying anything more towards the property. You have no legal liability for it and if you're not going to benefit from any payments there's no point you paying. He could even be using you, deliberately waiting until the mortgage is paid off by you both, before kicking you out without a penny.
If you're splitting up and haven't already done this, you should split finances completely. So your wages go into solely your account and you buy food for yourself not him, you both chip in for DC (because they're his) and utilities/council tax like you would with any other house-mate.
I'd turn the living room into a bedroom for yourself too, if there's no other rooms. You're effectively a lodger, whether you're paying half the bills or paying eg £150/wk rent and no bills. Lodgers have no rights by the way, so he can still kick you out with a week's notice. If you get him to give you a Lodger's Agreement (can't remember exactly what it's called, templates available online) you can claim help with rent if you're on a low income, through universal credit. No more doing his laundry or cooking either and only your fair share of housework.
You'll get more sympathetic help from authorities if you've obviously split up. Living in the same bedroom and sharing finances etc, you're basically still in a relationship in their eyes.
Your 18 year old should look on the Entitled To website as well when they get a job as they're likely to be on a low wage. Over 18s are adults and not their parents responsibility. They are their own household regardless of where they live. Although they're only entitled to a shared house rate of housing allowance, not a one bedroom property rate. It'll still help with the rent though if they live with you. You'd need to put them on the tenancy so they'd have evidence of liability for shared housing costs.