I've been there and done that. When I found out she was married I hit the door running.
No not all relationships are life long some are just friends with benefits but is that really a friend you want. What kind of friendship can be based on lies and deceit. You know she is capable of it. How can you honestly look this person in the eyes and think that she is telling you the truth. You never can.
As far as the husband goes, don't judge a book by it's cover. If you corner any animal it will defend it's self. Emotions do crazy things. Break a mans heart and who knows what he is capable of.