Feeling down ..

My ex boyfriend and I have been over almost a year now , and he moved on the next month we had broken up . Long story short it was one of the most yet toxic relationship ever but I can’t seem to let go . He brings his girlfriend to our church that I still go to and it breaks my heart every time . Just found out he moved in with his new girlfriend and I can’t seem to understand how and why he moved on so fast after 6 years . Sometimes I catch him staring at me and I can’t seem to understand anything im still damaged .. if you guys can give me some advice please do so thanks ...