Advice needed ASAP - relationship

So my now ex-boyfriend and I dated for seven months. He broke up with me because he didn't want a girlfriend anymore and thought I diserved better than him. We kept talking after the break up and continued hooking up. He said that he just wanted to have fun so I told him we shouldn't hook up anymore and just stay friends. That was Monday. Wednesday he texts me and tells me "hey you looked really good today". He flirts with me at school all the time and acts like nothin is wrong. But I just found out today that my ex best friend and him are now talking and are going to hook up (sex). I also found out that he told the whole grade how many times we had sex and all the details about it. Which is super embarrassing. I'm so confused I dont know what to do. He said that he wantes to get back together with me but not in the near future, because he doesnt want a girlfriend right now. He still flirts with me and treats me special but is apparently talking/ hooking up with my ex best friend... What do I do ? :(

he is just a flirt ,does not respect your feelings,avoid him