Trouble moving on

My boyfriend and I broke up about two weeks ago and I still feel terrible about everything. The hardest part is that I know he’s doing great and that he’s already moving on. I know that it’s selfish for me to think that way, but it feels like he never even cared about me if it’s so easy for him to get over it. I just wish I didn’t feel so heartbroken without him. Have any of you ever felt this way? Any advice?