From what I've read from bioware's blog and short tales the red lyrium being given to templars started after Cullen left Kirkwall, they posted this samson story thing there. So in-game we assume it happens while he's there thanks to viscount Hawke's little story but according to short story done by a bioware writer it happens after Cullen leaves, and remaining Templars flounder from having no actual orders. We may never be told the truth of the red lyrium timeline sadly so it can't be used in any canon fact debate, seeing as Bioware's contradicting itself haha.
http://blog.bioware....ry-paper-steel/
There nothing stating he was the first to drink red Lyrium
I checked on that. Forgot about it.
However, you can't compare Hawke's connections with Cullen's. And it's not like red lyrium was just sitting there right in the open for everyone to snort it at their leasure. He had other priorities and got negligent with the whole red lyrium thing. But the way some make him out to be, is like he's at fault for the entire mess the templars got into.
No he isn't at fault for the entire thing, doesn't mean he has no guilt.
After such display of incompetence he should have not become the Inquisition general.
And I can compare because Hawke wasnt at Kirkwall and know about it, Cullen was at the Gallows and didn't know.
I think the whole red templar thing in kirkwall is a huge plot hole. If the red templars were that aggressive to drive viscount Hawke away, why didn't anyone in power do anything? Not only Cullen, but aveline, varric, the nobles, the city guards, remaining templars, and also Cassandra and Leli when they came here. For the mage ally Hawke scenario, Hawke didn't really explain when they discovered the templars been taking red lyrium, which could be after Cullen left.
That being said, I don't think Cullen is a deserter legal and military wise. While if he left some of the remaining templars (as some of the templars joined along side with him, e.g. that captain stationing at the Griffin post) to whatever they might face is debatable.
Yes its a huge plot hole and bad writing.
If the red templars had small numbers, Hawke could have handled it with the City Guard and the uncorrupted templars.
If they were a large force, it would be impossible to Cullen to not know.
It doesn't matter when Hawke who allied with the mages discovered it, the corruption started before he left, Cullen left them to be corrupted because of his negligence.