
"I can't do this" is. A perfectly fine way to say you're not ready for a relationship, should he have explained a bit more, maybe, but if he doesn't feel comfortable sharing trauma with someone he doesn't have to.
The only thing that's unreasonable is Kyousuke's reaction. Think about it you're saku; you've broken up with this guy presumably due to trauma reasons. He then pines over you for 2 years & is always watching you distantly but never reaches out to you to clear up what happened despite you saying you wanted to be friends. Then gets dead drunk so you help him, after having his friend blame you for his pitiful state.
If Saku didn't clearly still like Kyosuke that'd be so awful. Thus whole scenario would be so creepy.

It was Kyousuke's first everything so when everything ended with a "I can't do this" it was too vague especially because it seemed to go well just a moment ago.
The fact is that both of them watch the other but neither reach out , or they don't do it in the right way.
It's painful to see them like this.

What a lot of us readers are upset about is his two faced behaviour. Saku claims he wants to break up abruptly without any explanation (causing Kyousuke to feel that it's his fault they broke up) and says he wants to return to being friends. Then, later he feels entitled to being jealous and saying snide comments of 'you've slept with her once or twice' about Kyousuke's female friends despite setting his boundary as Kyousuke's 'friend' only. Now, he's spouting bs about 'not having played with him' while taking Kyousuke (who clearly still has feelings for him) back to his house. Having a trauma does not excuse enforcing negative experiences on others and certainly doesn't excuse toxic behaviour. If his trauma is so deep rooted, he should consider therapy rather than continuing to sleep around with strangers and manipulating his childhood friend
Hate the sister wow disgusting. The only people who are ok with the sister don't have siblings or are cretins.