Moving on after a break up

My boyfriend and I broke up after a year and a half because we were taking each other for granted and needed space and time away. We were very serious and we thought we were going to get married. We didn't talk for a few weeks and now he's already texting one specific girl and have hung out once. He says they aren't "talking" or anything but "possible potential" I still feel hurt that he could jump into something else so soon after our relationship. Why is he jumping into something so fast? Need answers! ❤️