I often think about how hard it must have been for Akechi and Ren to fall asleep peacefully at night. They would return home after their "dates" and Akechi would lie there thinking about how soon it would all be over, and he’d be alone again. He thought about how bitter it would be to betray and kill Ren, even as he tried to convince himself that this was exactly what he had to do to achieve his goal. Before, he considered himself a fool whenever he opened up too much to Ren, but now all of it was starting to feel meaningless - because Ren was going to die, and he would take all of their shared confessions to the grave with him. Akechi tried to comfort himself, telling himself he was used to it, and that, ultimately, nothing mattered more than taking revenge on Shido.
Ren, in his own way, was also thinking about the end of their connection. He probably didn’t even know what to think - his thoughts must have been tangled, and he tried not to dwell on it too much, because now wasn’t the right time. After all, it would be strange to grieve someone who was responsible for the deaths of his friends’ parents.
But how terrible Ren’s night must have been after the engine room. I don’t believe he just fell asleep after that monologue about revenge. He must have replayed every word Akechi said over and over in his head, and after Akechi’s death, his emotions simply refused to leave him alone. He lost someone close to him - someone he had feelings for that went beyond friendship. Even if he understood how things were supposed to be, it all felt absurd, considering they stood on opposite sides of the barricades.
And then the third semester comes, and Akechi suddenly returns. Ren’s mind and heart must have been overwhelmed with emotions - he missed Akechi so much, but at the same time, he understood that once again, this wasn’t the right place or time, and he had to push his feelings aside.
This time, it’s Akechi whose thoughts fall into disarray, because now he doesn’t know what to think either. A perfect reality where he is alive, where he’s directly told that he and Ren have a chance to start over - but even that turns out to be a bad option. Because even here, he becomes an object of manipulation, a tool used to manipulate Ren.
Ren realizes he can’t go on like this. He starts to open up to Akechi, showing how much he truly values him, but in the end, he once again finds himself in a situation where his feelings might betray him. And Akechi understands this too. That’s why he can’t bring himself to listen to Ren - he has no choice but to give Ren a choice, and then simply walk away, hiding from everything.