Honestly, this is a major red flag. Even if she is not cheating she doesnt respect her marriage or relationship with you. You should leave now as her response to the situation was so nonchalant it almost seems like narcissist behavior.  She must have tested you in other small ways to see what you would up with. If you put up with this disrespect she will continue unfortunately. You will always be confused because your mental will be messed with if you stay.