I'm sort of an old fashioned kind of guy

ころとん

All the way back in chapter 14, Twilight acted quite callously toward Yor by bugging her clothes and then cornering her as an SSS officer in disguise.

She took him completely off guard with her defensive reaction, willing to fight the SSS on Loid Forger's behalf.

This led Twilight to waver in his conviction and feel bad about what he did, as Franky observed:

More than 100 chapters later he realizes in a panic that his actions have come back to bite him. Yor might recognize Lieutenant Curtis and who knows what she might say in front of a house full of SSS agents, or what she might say to her brother or someone else in private later. Any doubt on her part could eventually lead to suspicions against Loid Forger.

So he doubles down on the "do whatever it takes" mindset. Doesn't matter if he has any affection for Yor at this point, he'll tranquilize her if it means escaping this nightmare he's created for himself. His brain is so overtaxed he can't think of any other escape plan.

And he actually goes through with it (though unexpectedly for him, Yor is immune).

Luckily for him, he's able to get out of the party with no one suspecting anything, and when he subconsciously recognizes he's safe, he almost collapses. Again leaning on Yor (literally) as someone he can let his guard down around.

Now we see the look of guilt once again. And not just guilt, but yearning (the sparkle) and the deep sense that he doesn't deserve Yor's help and care. If she knew how he'd mistreated her -- bugging her clothes, threatening her as an SSS agent, and injecting her with a tranquilizer -- surely she wouldn't look at him with such compassion. When he says "I'm sorry," he means it.

I wonder if just like in chapter 14, Twilight will have a conversation with Franky about what happened. It'll start off as a rant about how Franky's watch didn't work and he's cutting off his R&D funds, but when Franky makes him explain what exactly happened, maybe Franky will be like "Wait a minute, you used it on your wife? That's cold, man!"

"She's not my real wife, it's only for the--"

"Are you serious, that woman has done more for the mission than anyone other than Anya! And me, you better not forget--"

To which Twilight will probably snap back in anger because he doesn't know what to do with all his guilt. In order to cover for the shady things he previously did to Yor, he just did something even shadier, and he'll wonder if it'll just continue in this vicious cycle. It's worse now because he actually feels something deeper for her. He's simultaneously willing to stand in front of a loaded gun for her, and to knock her out cold in order to survive.