Unfortunately, ED is a major factor in my SSM sitch.... And, although my husband now willingly talks about it, things had to brew to a crisis point before he would face the music.
I'm sure your H is in turmoil right now, especially if this has cropped up suddenly for him. Many men view ED as a blow to their masculinity and react in some very non-constructive ways. Although he may be tempted to go for the shortcut--pills (Viagra)--he should first try and pinpoint why the ED is occurring. The faster you figure that out, the better the chances of "fixing" the problem.
For my H, figuring out "why" was easy (and in order of probable relevance for him): 1) lifelong smoking; 2) overweight; 3) sedentary lifestyle; 4) lifelong issues with PE (premature ejaculation); 5) psychological--anticipation of a problem getting an erection; 6) prior cancer treatment in the pelvic area. He has so many things factoring in that ED may always be his struggle.
I highly recommend the book, Overcoming Impotence by J. Stephen Jones, MD. Written for "regular guys" by a urologist specializing in ED, the book was an easy read, humorous, and VERY INFORMATIVE. It talks about everything ED related, but in a way that offers encouragement. My H actually read it cover to cover and is (maybe) now motivated to finally schedule a Dr.'s appt.
ED is often God's way of telling men that something's going on in their body, and they need to check it out. It may turn out to be nothing, but the book states that the male equipment is the "canary in the coal mine" for a health problem, so get the book and read it yourself first. Perhaps he will be willing to read also....it will really help his peace of mind, I think.