If you have morning erections and the like you're ok on the physical level. Ms can even increase their frequency and libido as well as diminish things. But successive performance failures is a sign of something. Consult a physician. Literally anything can crop up with ms as the cns is all you are physically, and ms has a mind of its own relative to its path and the locations of demyelination. A full neurological evaluation is needed for diagnosis of ms. And you need an ms specialist rather than a generalist.