Why is he jealous if he told me he doesn’t want a relationship

Princess

‭ So I’ve liked this guy for ages I told him a month ago how I felt and he sed he just wanted to be freinds now I’ve told him I have a boyfriend he turned around and says err why am I speaking to u then and told me I was cheating and that I’m a cheat because I’m speaking to him and I says ur my freind so of course I will speak to u why did he react like that