From a woman's point of view, I believe having a sexual relationship with a taken woman is a bad idea, unless the husband/partner gave his consent.

I agree with Rossie. For several reasons. If the husband finds out, and is a jealous person, and worse yet a violent person, you could be putting yourself in danger. Then, often you face the possibility that if she cheats on him, if you are looking for a relationship, she will probably do the same to you. Also, you could break up the marriage, and unless she is being treated poorly (and often, women who are trying to snag someone else will lie about their situations, although that is NOT always the case, but it DOES happen - I have a friend who does this...often...) you could cause some conflicts between them.

I suppose a lot depends on you, her and the husband.

No harm in wanting something. The harm comes when you hurt someone else by acting on impulses. If the husband isn't into "sharing," acting on those wants isn't the best route to take.