How to help my ADHD partner to get back his sexual desire?

As I wrote in others post here, my marriage is improving and everything is going great. The only thing that keep me a kind of frustrated, although I have learned how to deal with it through the years, is that he lost his sex drive since we got married 6 years ago. We tried medications, therapy, doctors, but nothing helped him. I almost did everything to wake up his fire but nothing looks to help. He feels bad about this too, so, he avoid to talk about it. He's charming and shows me his love in many  other ways. We love each other and I have hope that one day he can get back his sex drive.  Any of you has gone through a similar experience? Any suggestions? What do you think?