Your plan would give him far more than his fair share.
Yes his deposit should be given back to him at +30%.
For each of his half of the payments, the majority of that money went to paying interest on the mortgage, that is a servics he received and paid for from the bank, he doesn't get that money back. If he did he would have been living rent free for years. Not reasonable.
A small slither of each monthly payment wwnt to paying off the mortgage and he should have a fair slice of that. But it will be WAY less than what you propose in your OP.
On the day you bought, the value was the price you paid and that was made up of equity that was your deposit, his deposit and the remainder was the mortgage money from the bank.
As you split, the value now is made up of equity that is the increase in value of your original deposits, equity that is the result of the anount of the mortgage amount owed that has been paid off, and the remaining amount owed to the bank.
So check what the bank says is still owed, and subtract that from the original amount of the mortgage. Call that value A. Your ex gets half of A if he has been psying half the mortgage payments.
The rest of the equity (realistic house value minus outstanding mortgage minus A) should be split in the same proportion as the amount originally contributed to with your respective deposits.