can't you be happy for qingy? his father awake and he looks so happy. he was happy to live...

because he wanted the father dead, and his plan failed

It's becausehis mother still haunts his dreams when he does not take revenge for her

Hw could he kill his lover’s dad. From wht i read, qingyu papa looks kind & soft. Is he idiot afraid of ghost?

I think it's something like : qingyu'mother seduced my father leading my mother to commit suicide, but she's dead too so I'm gonna destroy her familly instead like she destroyed mine (his father probably played the victim).
The mother's "ghost" represents all his suffering and his guilt for failing to prevent his mother from committing suicide, it "eats him from the inside".

Here few types of ppl.
1. Cheng’s dad (act like he’s a victim but he’s a real asshole)
2. Cheng (he think he’s suffering enough & put all fault to the qinyu’s mom, he’s blind by his mom grudge.
3.qingyu (a victim of chengs. a kind boy who always trying to be positive in any situation)
4.qingyu’s dad (a victim of all situation, a kind & good dad)

The different is these 2 father. Cheng raised by his uncle. Qingyu by his dad. You can see 2 type of personality. Cheng choose his path to be live in grudge eventho his uncle treat him kind. Qingyu was a carefree & happy boy bcoz his father gave him love & full attention.

Cheng hate the fact qingyu has a happy life & he has none. So he was eager to revenge him eventho going far to kill qingyu’s dad. This is the problem. He did worst thing as it wasn’t wrong at all. Its like “they deserve to die bcoz they make me suffer”- he chose to live that way & blame others of the consequence. About his mom, he’s old enough to think which is good or bad. He’s psychology lecturer after all but he is a psyco.