so your ex has a boyfriend/partner
and he owns an asset (property) which he is going to sell so your ex can raise the money to buy you out
and she never mentioned this at the final hearing? Have I got that right?
Nobody online can give you an exact answer. It depend on so many factors.
In theory, yes, a court final decision can be re-opened if one of the parties failed to give full disclosure of relevant facts. But in your situation, I think the question you must ask yourself is "what difference would it have made to the decision?".
If your ex is going to buy you out, then I assume the court divided your former home into shares, for you and for her.
Would that division really have been different? It's unlikely, for example, that the court would say "ok Mrs Ex, you have a partner, you can live in his house and we'll give everything to Mr Ex". The chances are the equity would have been divided the same way with or without knowing about ex's partner's asset.
And presumably there was some discussion at court about how/when the house would be sold to release your equity; so if your ex can buy you out sooner, that's a better deal for you?