I think this is not mababaw. I definitely understand why you felt that way. I totally get your point why you got offended. You are together so you expect him to focus on you and not be attracted to another woman. You are pregnant so there are body changes that you cannot control. It is unfair for him to tell you that this is kakitiran ng utak or kababawan. By assessing naman the side of your husband, check mo kung ano ang top emotional needs niya, kasi it seems like one of them is physical attraction. Sa couples kasi, both of you have to meet each other's top emotional needs and love languages. When you meet them, both of you are happy. Pero sa case na ito, it's quite unfair dahil kung need nya ang physical attractiveness, hindi mo ito hawak dahil sa hormones mo.
As for separating, I think you can talk this through muna pero both of you should calm down first.