Welcome to the board!
I second Ellie. Give him information about the disease, explain why your ex was diagnosed with it in a clinical way, in as non-scary and non-judgmental a way as possible, and let him ask questions. By the way -- what does dad think about this?
Co-Moderator, Bipolar Forum
It is a melancholy of mine own, compounded of many simples, extracted from many objects, and indeed the sundry contemplation of my travels, in which my often rumination wraps me in a most humorous sadness. -- William Shakespeare