It's not right to be compared constantly to "the ex"

Having a heart to heart talk about it will be necessary. I dunno him and I dunno you so I'm not sure how you'd go about it.

Maybe coming from it at an angle that doesn't include "the ex" would be good. That way it isn't about HER it's about YOU. Perhaps discuss his views of psychotherapy, of your dx, of your meds if you have any. Discuss YOUR issues and what HE feels about it. If HE brings her up, then respond to it with "I'm not her, but I still respect your experience and feelings"... kind of thing. You can also drop it in at the end, expressing understanding that it's hard for him to go through this because he's had a bad experience in the past, but to reassure him that you are YOU, and that the situations are totally different. Different people, different stories.

Dunno if that helps, I'm a bit relationship-ex-confused myself =)