Move on from this petty middle school bs man. It’s nearly a decade in the past just let it go and be an adult. A middle school feud shouldn’t have this much power over your mind.
Make sure when you cum, you scream (loud enough for him to hear) “THAAAR SHE BLOOOWWWWS”
You and this dude my become close friends. Ignore him and just be a nice guy to her and her family. If you are dating her a while offer little olive branches. Do not go to battle with this guy.