OP your situation is quite complex.
From what you have posted you and your ex have a joint mortgage. The lender requires one or both of you to pay it in full. They don’t care who and they won’t recognise any agreement you made between you. The mortgage agreement trumps that. If the mortgage is not paid in full you both default. That will create a bad credit marker for you both. Which will impact on any future borrowing from any type of lender. But expect mortgage applications to be declined.
From what you have posted and reading between the lines you are both messing around with each other over money and in doing so putting your credit worthiness at risk. The only way to stop it is to wind back your positions and pay your bills. You are both also breaching terms in your mortgage and insurance by not living there.
From what you have posted he stopped giving you a contribution towards some bills. Reading between the lines I assume he did this because you weren’t paying half the mortgage. And in retaliation you recovered this by not paying 30% of the mortgage. And you are now both in default and you are both going to have bad credit ratings until you both back down.
You cannot insist he pays 70% of everything now you are apart. When you were together he agreed to pay more than his share of the bills. He didn’t have to and he wasn’t obliged to. There is no legal mechanism you can use to compel him to fund 70% of the mortgage or anything else.
Most people would expect to pay 50% now you are separated. He subsidised you because you were together not because he has to. Now you have split you need to pay your share which is half. The fact that he earns more is neither here or there.
It is a simple principle you own half and you live in half and you benefit from half. It is only right you should pay half. Not being together means you cannot expect him to pay part of your half.
In the event that one of you lives on the house that party should pay the full mortgage because they are benefiting 100% from the asset.
Not paying the mortgage is a problem for both of you. Not living there is a problem for both of you. Problems you are creating equally for yourself and each other.
I can’t give him advice but you should offer to pay half of all the costs since you split if he agrees to pay the other half. Then you both need to agree the house should be occupied and that the person who occupies it should pay the mortgage.