Should I tell her or not?

Hey ladies! I'm in a bit of a delimma. So I was seeing this guy for 5 months and randomly he went on vacation and started dating a new girl who has apparently madly in love with but also lives in a different country. Right before his vacay he said he wanted to make it official with me with my family on Christmas and New Years. After I found out I was really heartbroken but eventually forgave him only for him to just go back there again and post her all over social media and tell me he's done. So months later he's texting me trying to go to dinner and have sex. Should I message her on FB and show her proof or just block him?