He doesn't like talking about it and I respect that although I think being able to talk about what went wrong is a healthy way to move on.
Otherwise I think it can be left to fester, particularly with men who never work out why they managed to ruin their relationship and then it's on to the next one.
Ah, you're one of those.
OK.
Excuse me whilst I step over and amongst the gender stereotyping...
You think talking about it is a healthy way to move on. He doesn't. He has his thoughts. He's probably well aware of what went wrong, has taken responsibility for his own part in it, has made decisions to not do X, Y or Z again if, in conversations between he and his ex, these were highlighted as issues.
He doesn't feel the need to talk about it and this is what gives "us women" a bad name - those who feel the need to pick apart and question and then get upset when they hear something they don't like.
Understanding what went wrong in his relationship with his ex won't help the relationship he has with you because relationships exist between people - they are a result of the interplay and interaction between the two people in the relationhip. If both people behave decently and considerately then there is nothing to be gained in you making him talk about the past.
If you honestly believe that he is one of those men who never work out why they managed to ruin their relationship, why are you bothering? It's not your role to 'educate' him; it's not your role to 'counsel' him. I would say that if you honestly believe he ruined his last relationship and lacks the emotional intelligence to not repeat past mistakes without the intervention of his 'woman', then why are you bothering?