“I must’ve been an idiot to think this could work! Of all the people I could've saved, I had to pick you?! I could’ve been helping… good people, people that deserved it! Now I’ve no more lives left and it’s… it’s not fair !” The words were out of the Doctor’s mouth before they even realised the meaning. After all those spans of very deliberately not saying it and all the effort expended to shield their memories of the event from the Master, they’d just come out like a colossally thick, bone dead stupid dunce, and told him what they’d done. They grimaced in horrified embarrassment.
Of course, a fraction later, it also dawned on the Doctor that they’d just said something probably unforgivable. This was, technically, worse.
The Master was stunned to silence, for once. Normally his silences were by choice, or a sign of feeling unwell.
This had been one of his good days, and over several cups of coffee (tea for the Doctor) it had seemed amusing to debate them over some point of intergalactic history that shouldn’t have had any personal attachment for either of the two. But something had gone wrong (they’d misjudged each other’s moods? the worry that always underlay everything had surfaced as tension?), and badinage had turned to acrimony for reasons that had little to do with the topic at hand. A few insults had been exchanged, the Master had said something especially ungrateful…
And that's when the Doctor had blurted it out.
The Master didn't even make one of the overdramatic faces that he'd sometimes use when pain or noise got so distracting that verbal language didn't come easily. He just briefly made eye contact to confirm that the Doctor wasn't cracking some bizarre joke, opened his mouth, found no words, closed it again, found nothing to 'say' telepathically (just static, louder and louder), got up, and shuffled out.
The Doctor sat with their head in their hands.
How could I be so stupid?! Must go after him. It’s too late to go after him. It's too soon to go after him. What would I even say?!
Only after the Master was long gone did they remember the white noise of pain rising on the shared wavelength and realise the incident had probably triggered a flare-up.
He really shouldn't be alone. But would he trust me to come near him, now?!