This is so easy. It was never meant to be (you two I mean).
I sounds like her marriage wasn't meant to be either. She could very well want to romp your bones though so next time you are out drinking with her ask her if she wants to go to round two with you and some friends at the dance club. Assuming you live in an area with decent clubs and that you and her would be into dancing. Where I live this is very applicable.
If she says yes then it's a pretty good sign that she at a minimum wants to test herself of live on the edge a little. She may very well know that she wants you to slip it to her. Get both of you some drinks and start dancing. Look for her signs on the floor. You may not know what those signs would be, but if she stares in your eyes, grabs your hands, puts her buns on your nub or anything like that then you have to respond and take it to the next level.
Bring her in tight, let her feel your chubby rub up so she knows where your head is and maybe get some cheek to cheek going where she is wondering (and liking the idea) if you're going to possibly kiss her. Of course you won't.
When you think she's good and juicy, ask her if she wants to take off. Simple. If you have gotten to this point it is on.
From here I predict, wild & passionate secret sex followed by an uncomfortable break up. You may do things that you never imagined and that she could never get her husband to do. Just make it clear from the beginning that you find her extremely sexy and exciting, but are not in it for love. You are happy to be her workout partner if that is ok with her, but your not trying to sweep her away or break up her home. That stuff is for her to decide.
Plenty of women get into marriages that they really shouldn't have that serve well enough as partnerships but lack passion, love or excitement. You may be able to give her something that is lacking, but don't try to take her away.
Good luck and happy slapping.
The Pro