You could tell him what you just said to us, that you're confused. Tell him that you don't know how to move forward without closure, and in order to help/support him you'll need honesty past and present. If you didn't love him you wouldn't be there trying to work it out, so let him know that. If he thinks you're holding some malicious grudge rather than trying to understand him better he may feel some latent shame and become defensive, or just act adversarial.
I think full openness helps.