I do not personally feel you are overreacting. I am not a party to your relationship with your husband, obviously, so I do not have all the details, but I completely understand your feelings, your perspective and your desire for him to stop doing what he is doing with this other woman. If the man in my life were doing what he is doing, I would dump him. But then, I have dumped at least eight men HAHAHAHA so maybe you don't want to listen to me LOL. (I hope that made you smile a little).
Try an Al-Anon meeting.