First and foremost, smack that friend of yours for telling you not to use Quelling. Black Mage pulls absurd amounts of aggro, especially on the onset of a pull. You will be riding extremely close to even decently geared tanks-- if not pulling aggro entirely-- without Quelling. With that aside, it sounds as though you had a Paladin who doesn't quite realize you can't just spam Flash a couple time and hold threat the entire time. I partly wonder if they are coming off Warrior or Dark Knight where multi-pull threat management is significantly easier due to Overpower and Unleash/Abyssal Drain dealing damage in addition to aggro generation. Regardless, this is a tank issue. If you are using Quelling and still pulling hate, they either aren't generating enough threat or you simply out gear them enough they literally can't hold it. Was this Paladin in Ironworks by chance? If so and you were in more appropriate gear, you're the tank no matter what they do. And that's still their fault for queuing into a dungeon with gear significantly below level.

What stands out to me is how you held higher aggro over the second Black Mage despite utterly gimping yourself. Seems like this couple are equally bad players and came across someone who actually knows how to Black Mage. Rather then acknowledge maybe his girlfriend needed to rethink her rotation, he blamed you to make her feel better.