Boyfriend drama

So my SO is friendly asf he thinks texting his exes and being cool with them when we aren't talking is cool at first I thought I was over reacting but once you see the messages like didn't you just say she was annoying and now that we are on this "break" he thinks it's single all summer 16' like if you wanted to be single for the summer then say that don't have me looking dumb when I'm really trying to be down for you if you think screwing me over before I do you is smart it's really not I just need some type of advice bc this is getting waaay too stressful😔😫