Okay, does anyone think think that Qu Yuan's extremely self righteous behavior is going to cause a f*** ton of problems later?  He is noble and justice but lacks empathy in dealing with people who commit crimes.  Here is a list of things I am sure he will regret, or as I like to call them, 'WTF was I thinking?' moments:
1.Cang Yun.  
Hardly perfect, no one is.  Qu Yuan could have easily had his marriage issue resolved if he assisted in helping him pass the examination.  Even the King liked him.  But Qu Yuan's standards in poetry are impossibly high because he judges others based off of his own skill (as Bi Xia points out)--who could ever pass?  He destroys this guys last hope.  Cang Yun, who has been tossed out of the Zhao family and maimed simply gives up and resorts to gambling.  Of course we learn later he is far from perfect nevertheless it should have been Bi Xia who had the right to choose him or reject him; she should have that control to ruin her life or not.  Now she wants revenge.  
2.Lord Jing
We all know him as the ringleader in that annoying trio of criminals in Quan.  The brains of the bunch.  Later we learn that he has been committing his crimes to help his uncle, the head of the family, who also raised him.  Whether it is to repay him for raising or not, who knows, but what we do know is that he has been actively amassing the Jing family fortune.  I imagine some of that is related to Jing. Now this doesn't excuse criminal acts.  But the most important piece in all of this is that Qu Yuan could have carefully cleaned up all of this by setting them up and having them incriminate themself.  They would have had all the evidence.  But he arrests him, tortures him, because he can't tolerate the injustice of someone he knows is guilty to be free.  Well.  Now this has blown up, the king is involved, and it makes it harder for him to be with his lady love since his father, Father Qu, is now against it 100%
3.Mo Chou
Qu Yuan lives in a time period where a man can have multiple wives.  I am all for true love.  But this is such an easy way out.  however, true love.  It appears in dozens of dramas.  But Qu Yuan is a man of principle, and as a poet, he is a romantic.  He absolutely refuses to marry anyone but her. Okay. Even if he never once sleeps with the other woman.  He still refuses.  Okay. Fine.  But even Ye Hua got married to someone else in eternal love, even if it is a marriage in name only.
Qu Yuan is creating more and more enemies simply by choosing to be with her (Like the Zhao) but he could clear that up if he had two wives but this is a drama about true love.  So we know this might not end well....
  Finally, his efforts to carry out justice constantly endanger his lady love.  He is lucky she knows how to fight, because she saves his butt a lot.

-At the end of the Day I still like the show because i can't WAIT for all of this to crumble around him. I have a feeling the show is setting up for this.  After all, the leads fall in love quickly and they constantly say things like 'nothing can keep me from you' and they often 'hope things will be like this always'.  That is standard for: later on, we will be separated, things will never be the same, and holy moly I am filled with regret and remorse.  I can't wait for Qu Yuan's self righteousness, his sense of knowing all the answers, and his actions to bite him back because he is riding very high right now. In a drama that can only mean one thing: everything will not just come crashing down, it will be annihilated with ten atomic bombs and 50 H bombs.  mwahahahahaa 
.....I seriously can't wait.  
Sad that i dont saw this tread more early. 
And Yes, Cang Yun was the most regrettable one. With the Zhao's Marriage out the picture, he could be married to Mo Chou. But its his personality, he cant compromise (But, ironically, he CAN compromise when comes to the other states.). For me, he is a hypocrite in the beginner. 

And even his brother says that: "He can have Mo Chou as a concubine". Political Marriage was very common in that time, and he, a scholar, should knew that. But as you said, he is a man of principle. But he should compromise. Its nothing wrong about that if you want to be with the woman that you love.