The first instance sounds like it's completely unrelated. It's a different day. A legit PK. You lost the fight, you lost some stuff. Not a problem. That's the name of the game (literally). Moving on...
The next day, you say he took a full con from you within 3 hours. Was that 3 PKs or was it 2 PKs and a familiar kill? Based on your earlier comments, its the latter. 2 PKs in 3 hours (plus a familiar kill).
I think we can all agree that 2 PKs in a 3 hour timeframe isn't bad. It's a PK game, you're obviously enemies. He isn't even stealth, so you have ample opportunity to escape (if you're being careful). In other words, 2 PKs separated by 3 hours of playtime for both if you is definitely not griefing. Moving on...
That leaves the familiar kill as the only real part of this scenario that could be considered "griefing". So what are the circumstances surrounding that? Was it during the PK that it died as well? Was he off doing something else, and your familiar snuck up on him? Did he walk up to you, kill your familiar, and ignore you entirely? What actually happened that makes that specific familiar kill "griefing" in your eyes?