That is a pretty good suggestion, especially if "stressed out lately" is a phrase he's been using for years. Maybe it has nothing to do with BDSM, and he really has other life issues to work out (when a person has something eating at them other things tend to fall by the wayside, sex included). Maybe you could try asking if he'll see a therapist, or if you can go together for couples counseling (so that it's a thing you're doing together).