When Theo slipped into his time at the brothel it was pretty easy to predict. It gave Theo the least stress than any other time in his life before he'd met Ax, even if it stressed out everyone around him, anyone who had the misfortune to trigger him.
When Theo fell into the past, into his childhood, it was horrible all round but easy to spot. There was no hiding the abject horror, the intense terror and the blank hopelessness at the inevitability of what was going to happen to him.
But these falls into his school life were insidious. On paper it might have been the better of the three, but in experience it was just as bad. It was easy to overlook in Theo's quieter times, and it didn't scare or disturb people as much as his other slips, but it was still a horror to Theo. The sheer pressure cooker of his school life eventually led to his nervous breakdown and whenever he went back to that place he'd end up with muscles in tension for days.
The veneer of normalcy was exactly how he'd been during his schooldays, so it made sense that it was difficult to catch unless, like Martin, you saw that change from relaxed and honest to stiff and unhappy. It spoke to how close they'd become that Martin had caught the change, and then the way he responded to it.
"I don't think I'm qualified to tutor." Theo admitted, those self-esteem issues present even then.
As important as maintaining a distant, aloof fake personality, there was a definite blip when Martin mentioned Ax. Theo stilled for a moment like he'd been put on pause, and then rebooted. "Oh. I- I don't know an Ax?" he said, but it was definitely more of a question than a statement.