I mean yeah... He was more consensual in the previous chapter
He does ask, if a bit teasingly, if he takes it out this much is it better. He gives Sooyoung the option to say no this is over. I don't doubt for one second he would.
Taesung is clearly good at reading the situation. He knew Sooyoung was having a panic attack when he saw Jisung, he knew that if he kept going that Sooyoung would pass out. At the same time, Sooyoung is saying stop, he's is touching himself.
It's hard because you're conditioned by bad tropes that everything is a hard no. And it should be accepted as such But Taesung, as we know is doing everything he can to woo Sooyoung. He isn't going to push his boundaries into a bad place (see Jisung). In this instance, it's more like he means slow down.
Am I the only one who thought the sex scene was borderline rape? Sure the scene was good but it was still rape...
Give the kid a break my guy