Why is he acting like this?

For a few months I have been with this guy who really liked me. We werent together, we wanted to take it slow. But we had good times, like kissed and all. It went on for ages and we were both really happy and making future plans to date. Then all of a sudden last week he started avoiding me and wouldnt text me. I dont know why or what could have happened. But it seems more than he just lost interest. There is definitely something else. And he wont explain anything to me. He told me to not text him. I told him I want to still stay friends atleast. He said ok but he still avoids and ignores me. What could be reasons for him to act like this? He claimed what he was doing was stupid and he stopped. He said it so half heartedly and wont even look me in the eye. Can someone please tell me why it could have gone wrong all of a sudden? He refuses to tell me.