I agree, he needs to make a decision, once and for all. Isn't it scandalous, enough, from his work perspective, that he's a married man, carrying on with another woman? Not that they know that, but which is worse? An affair of the heart or a divorce? Divorces are commonplace, have been for a few decades, now.

He sounds like he's afraid of confrontation. If he's unhappy in his marriage, which by the way, carrying on an affair is not a behavior of someone that truly loves and respects his wife, then it's time for him to own up to his marital dissatisfaction. Or let you, proceed forward in your own life, free of his inability to make you his number one priority--which if he truly loves you, this is a no brainer.