LRT the topic of YQY and SY being direct foils is something I (and a couple of friends) have been thinking on for a long, long time, thanks to many hints scattered throughout the novel. I'll jot down a couple and explain some thoughts, a thread:

1) YQY's and SY's being the only deaths in the novel confirmed to involve their swords shattering
2) The lead-up to their deaths above, where YQY and SY confront SJ and LBH respectively, directly parallel each other
a) YQY/SY accuses SJ/LBH of killing LQG/GYX

b) SJ/LBH saying that YQY/SY have already made up their minds regardless
c) YQY/SY wishing to "end it all" with their deaths
d) SJ/LBH realizing it's futile to talk, and each issue a command: "Get out" vs. "come with me"

3) SY's realization at the end of the story involves directly putting himself in YQY's shoes, going from "why didn't he say" to "why didn't I say"

4) (a fun one) MXTX's personal nicknames for each: she calls LBH Bing-mei and SJ Jiu-mei respectively, but she never addresses YQY as Qi-ge like one might expect with theme naming: she calls him "Yue-zhangmen." She calls SY "Shen-laoshi."

Now touching on a point LRT brought up: why didn't YQY speak? Cowardice is often cited, but I disagree. The biggest evidence is in part 5 of chapter 91, where YQY follows SJ into LX Caves to help him through his bottleneck (screen from pizzicatto's tl).

Here SJ is alarmed at YQY's OOC behavior: the normally-chatty YQY obstinately refuses to talk. But the key is this line when SJ demands him to speak: "What other reason could I have, other than fearing that Shidi would find me irritating if I spoke?"

The original Chinese “这不是怕我一开口，师弟你又烦？" is more blunt and concise, more like "Isn't it because I'm afraid you'll be irritated if I talk?"

This isn't a him being cowed; this is a very passive-agressive "shut the fuck up."

Like, "you're the one who always wants me to be quiet, don't complain now."

For whatever reason, YQY PURPOSELY DOES NOT want SJ to know about his qi deviation in LX Caves. He's shutting him down here. Hence the OOC. And right after, SJ is the one who's cowed!

He gives a weak comeback ("So you knew too!"), but also admits to wanting to talk to YQY. When he tries again, YQY doesn't even bother giving him a response other than an "oh." And SJ is described as "put out" by it.

YQY enabling SQQ is something that's very obvious through the novel. Less obvious is:
1) YQY tends to enable everyone: he let SQH's suspicious behavior after meeting MBJ for the first time slide, and then at the end of the novel he accepts SQH, who's a known traitor, back into

CQMS without any punishment

2) Whenever a third person becomes involved with YQY/SJ, YQY ALWAYS verbally sides with the third person. Examples:
1) YQY tells SJ to not go so hard on SQH (same part as above in the Airplane extras)
2) When LQG and SJ fight, YQY tells SJ he should

be kind to LQG first; he does not make the same demand of LQG back
3) In chapter 1, YQY requests SQQ to stop hurting LBH
4) In chapter 91 part 6, YQY tells an injured SJ who's already been tortured, "if you'd never treated LBH like this, today would have never happened."

So whenever SJ interacts with another person and YQY sees, YQY always:
1) assumes SJ's in the wrong (which may or may not be true)
2) shames him and dresses him down for his perceived wrong

The other party never gets the same treatment

Remember what SY does... whenever LBH and

CQMS come into conflict in the main novel, whether physical or over who SY's giving attention to, who does SY side with? It's never LBH. He tells LBH that his fears are unfounded, dismisses him as being too clingy. He scolds LBH for not addressing LQG properly.

He gets angry at LBH when CQMS is invaded, when LQG and YQY are injured during the siege. Of course part of it is because SY thinks LBH is invincible, but what about the words? He knows how LQG and many of CQMS address LBH. "Demon, beast." But he never calls them out for it.

Much like YQY does with SJ, SY always takes the stance that LBH is in the wrong, and follows-up with scolding and dismissal, asking the other party to better themselves. What kind of relationship does this remind you of? Because it doesn't seem like lovers...

It's "parents." More specifically, Chinese parents. When your kid does something wrong, common Chinese parent response is to:
1) apologize to the third-party with your kid
2) take your kid home and remonstrate with them; unless you're REALLY mad, then you scold them in public

In the beginning of SV, SY mentally refers to LBH as "this child," over and over. This address fades upon their first reunion, before resurging with a vengeance after his resurrection. Again, it's not something you usually call your lover! His opening up to LBH again also

corresponds to him mentally accepting LBH back as his child, once more. That is how SY sees LBH, first and foremost. The romantic stuff comes later.

I'd argue the same is true for YQY...and when we consider YQY seeing himself as SJ's "parent," an answer appears as to why he

refuses to tell SJ. When a parent goes through something very painful and horrifying, your instinct is to shield your child. YQ's damage was so bad his body had to be shattered and reformed. He doesn't want SJ to know how much he suffered, even if it means their resentment.

Like LRT said, both SY and YQY didn't speak about why they did the horrible things they did. Because they are coming from the position of the parent, who believes they always know better for the child than the child themselves. Before their kid gets a say, they've already made

up their mind: "this is for your own good." "You should listen to me." "Don't make a mess." "You thankless child, who was the one who raised you!"

"This is something unforgivable, and talking about it is pointless, because seeking forgiveness will only hurt them more."

Now that I'm staring at 这不是怕我一开口，师弟你又烦again, this captures more nuance:

"Isn't it because I fear Shidi will again be irritated as soon as I open my mouth?"

That "again" and that "as soon as I open my mouth"....nice and hostile