She likes you... she's married... now it's time to check your morality... and hers.
Do YOU have a problem with cheating?
Does SHE have a problem with cheating?
If you've answered yes to one or both of these questions then yes a 'relationship' is possible... but it will be ridiculous in it's complexity and potential for damage to you, her, and her husband.
Can't stop you from cheating... but I can tell you there won't be much good other than 'wham, bam, thank you ma'am,' .... it's easier to just pursue a woman who is single.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen