Why do I feel so GUILTY

My ex and I broke up about 4 months ago and the past few days I've been speaking to a guy I know from when we were at school. He's a lovely guy but I feel abit guilty (I know I shouldn't, we havent been together for months). My ex and I were together for 6 years and it feels weird talking to another guy cause I havent done it for so long. Is this normal? Or maybe I'm just not ready to be speaking to someone else yet..