Hmmm... Could be depression, could be ED, could be prostate, could be an affair. An affair is my least-likely choice unless the other things I mention turn out to be dead ends. Has his interest decreased gradually, or is this a sudden thing? How has his mood been otherwise? Depression affects people in different ways, and the signs show up in various facets of life. Is he taking any new medications? There are meds out there that can affect sex drive and function. Visit www.rxlist.com to look up his medications. Either find the med in the ABC listings or use the search window, generic or brand name doesn't matter. Once you find the med in the search results, click the med name. On the left there's a list of different pages for indications and dosage, side effects, etc. Whatever the cause, she needs to find the courage to talk with him about it if she hasn't already. Her husband is her chosen life partner and best friend, and letting this problem fester isn't fair to either of them. The hard part is doing it without laying blame or making an accusation. "I believe something is bothering you." Even if you KNOW you haven't, you can ask, "Have I done something wrong?" Anything that opens the door is worth trying.