I think only a lawyer could knowledgeably speculate if you would be entitled to more, and that would cost you for an investigation. I would suspect it would depend on 1) when your ex knew about the money and 2) the fact that he didn't include it (I assume) in his financial details, and possibly 3) the fact that you are now out of work. I think it might depend on the individual judge, if it goes to a judge.

I don't think it would be unreasonable for you to pursue it, yet it would also be reasonable to let it go and move on. I do think it's despicable what he did, however I don't know the legalities of splitting that kind of money.

I think the main thing is not to second guess yourself. If you want to pursue it, then do. If you don't, then don't think about it anymore.

For your mental health might be best to move on? As long as you're not going to "what if" yourself.