Should I block my ex on whatsapp?

Secret_girl
My ex started to date a girl just after 5 days when we broke up. They moved so fast. They put everywhere on social media their photos together I didn't feel ready for a relationship and I didn't date anyone else. I deleted his number and I didn't talk to him for 2 months later he wrote me and wanted to meet I refused later he wrote again he suggested me go to the same gym together although he was still in a relationship with that girl. I refused again cause it was not right thing for me. I said it But he said " yeah if she knew that I wrote you she would very angry but I think you should come" I was shocked. I dont know how I dated such an untrustable person. Should I block him? Is it sound like childish? Thanks :)
Should I block my ex on whatsapp?
14 Opinion