Undiagnosed but HIGHLY-probable ADD husband walked out unexpectedly. How to get him to go for diagnosis & treatment?

Earlier this week, my husband of nearly four years left me. He's been saying for ages that he's miserable, but couldn't communicate anything in an understandable way. It was all very nebulous, and I could tell he was really suffering and really frustrated. So was I, but I knew why I was unhappy--I felt like I wasn't married to a husband.

He would joke that he probably had ADD, and his mother agreed. Neither one of them really took it seriously. But after doing research and speaking to a therapist myself, there's no doubt--he's textbook ADD, I reacted in a textbook non-ADD spouse way, and our marriage fell apart in a textbook ADD way.

Right now, I just want to get some help for him. I have no idea where he is and what he's doing. He just took off, and I'm worried that he's going to do something impulsive, or burn some major bridges, and not just with me.

How do I get this guy to go to a different therapist, get diagnosed with ADD or whatever his problem and get the proper therapy if he won't talk to me, or listen anyway?