How to go about cut someone off?

Hi guys I hope your having a great day/ night!! I would really appreciate some advice on how to cut someone off in a somewhat nice way to remain being just friends. So the guy in question is some guy that I've know for a while and we kinda had a "situationship" but had decided to end it because of school ending. A few weeks after school had ended I texted him to ask something unrelated and we just kinda started talking and have been the whole summer. We text everyday just about random things and we sometimes flirt but then he goes around and tells me that he likes other girls, that I'm dumb, etc etc etc like a douche and I don't really wanna be in contact with him anymore. Today we had a date that he totally blew off and that drew the line. Pretty much the question is how do I cut him off? I'm not really good at these things so any kind of help would be very much appreciated!!