If this only happened once it's bad enough but if it happens on a regular basis you need to get to the bottom of why he's doing this.
One way coping if he does it again and after you've told him how you feel about it is to try this... ask him if he'd like you to introduce him to the other woman. Say that as he's so interested perhaps he'd like you to go and tell her all about him, adding that you can explain to her you've noticed he's always looking elsewhere. He won't want you to do it but you've made your point.
I think you have to tell him how much he's hurting you by looking at other women and tell him that you won't tolerate his behaviour - you don't have to.
Perhaps the two of you have lost a spark in your relationship and it won't come back if he behaves like this. Dress yourself up next time you're out together ( after telling him how you feel) try to be attentive yo him and if he's not interested even then you need to consider whether or not you want to waste time and effort on a man who's not pulling his weight in your marriage. No-one needs to tolerate this sort of neglectful behaviour.