Some people are naturally a bit flirtatious (me!)
... but I think it's only okay if you do it in front of the other person's other half.
Most girls find it flattering that you would want to flirt with their husband/BF.
If you flirt with the husband, and then turn to the wife and say ...
... "Do you need Josh tonight? If you're not using him, I'll look after him for you" ...
... the wife is amused, and flattered that her man is considered attractive.
BUT ... you should never do it behind the other person's back ...
... because then, it stops being fun, and becomes sneaky.
Text messages, for instance ... sneaky.
And, as you say ... showing no respect for the other person.
You do need to stop this woman doing this - or your husband does.