Sorry, it may make a significant difference. If it was your Petition, not his, then he almost certainly never made any financial claims in relation to your marriage, and by remarrying he has deprived himself of any right to make such an application. If that is the case, his only recourse is an application under Trusts of Land and Appointment of Trustees Act. In whose name is the home registered? I'm assuming joint names. If you haven't remarried, you retain you rights to make claims under the Matrimonial Causes Act, which (given the children are with you) is considerably more favourable to you.
As far as the agreement you signed is concerned, I think there's a fair chance this would be upheld. You entered into a mediated agreement, presumably on the basis of proper financial disclosure, and subsequently, having had the opportunity of seeking legal advice, confirmed that agreement by signing a consent order. Do you know why the Court wouldn't approve it? In most cases, IME, that happens because the statements of information in support aren't completed properly, so the Judge can't approve the order as s/he can't understand it, as there's not enough information about your respective finances.
The bad news is that you will probably have to go through a fairly gruelling court process to get there, but the Court should be keen to uphold the agreement: for public policy reasons, if nothing else, they don't like letting people renege on deals. And the delay should benefit you rather than him: you've stayed there all these years on the strength of it, presumably paying the mortgage and maintaining the home.
Get a lawyer, and go through the whole thing in detail with them, but try not to stress. From what you've said here, I don't think you'll be losing the house any time soon.