I think my girl dont even remember him, haha.. The last time my girl saw him is when she's 2 plus and now she's coming to 7 in 5mths' time.
Perhaps you can explain to your boy that mummy and daddy decided to go separate ways because we realise we are not suitable for each other. Please dont feel that our divorce has something to do with you, is not because of what you did/said. Both of us still love you.
Seriously speaking, is easier said than done. I think most importantly is to let him understand that he is not the cause of divorce and ensure him that you n daddy still loves him.