Was Jim high when he dumped her on the office? He didn't even dump her for Pam, just straight up treated her like shit and ditched her for nothing. She was a sweetheart and hot as fuck
At that moment, I think Jim just insecure. He has feelings for Pam but Pam with Roy. I think he's tried to make Pam jealous. And end up mixed with his feelings again at the boat. Just a bad day for him. She doesn't deserve to get treated like that, I agree.