He's asked me to go with him to his next counselling session and speak to the counseller without him being present. He wants to be sure I won't hold back to save his feelings so he's going to leave for a little while so I can talk to him.
The only problem with that is that when we aren't in the middle of a bad patch, I have a tendency to downplay or minimise his bahaviour, probably as a coping mechanism so expressing the damage caused by his illness will be tough.