It may be better to end YOUR marriage if this was Your situation but it's not so an alternative has been suggested that may just work for the two of them. I would suggest that he tell her what he wants to do first though and if she doesn't want him having sex with other women, then he either leaves her or she steps up and gets sex councelling. She can't have her cake and eat it either.. anymore then you don't think HE should.
Oh and dem's avise wasn't "bad" advise. You simply disagree with it.