Maintank (even paladin!) here and I beg you to not stop dps'ing! You were doing fine - a level 57 tank should have learned by now how to tank. If he didnt, its his fault and his fault alone - sadly its you problem after all but one that should be solved with a votekick after 2 or 3 attemtempts to explain to that guy what he should be doing (and yes, thats okay, SE said so themselves - and yes, I consider it harrassment if someone doesnt perform at least the minimum of their class, which would - for a paladin - be: Flash your soul out!).

It is true that you have to make adjustments to your own playstyle depending on the group - new tank? Might watch out to heal him a bit more since he doesnt know the dungeon. "Bad" gear? No CDs? Maybe even said something like "Hey, I'm a bit rusty"? - Probadly not a good idea to go full deeps on the first pull.
But as long as you feel confident with healing and dpsing - please, please go for it!

...if been running some libarys lately to get my DRK to 60 and I met scholars that were only casting heals, mostly physick. It made me cry. Healing me, while I got 90% of my HP left. While I was using CDs and couldnt really use my self-healing skills (which are pretty nice on DRK) because as soon as I got a scratch the healer would cast heals on me - instead of throwing around some DOTs... didnt said anything though because they were doing the minimum of their job and therefor "okay" - but a tank who doesnt even try to hold hate? Nope, not your fault.