Thace has a toplevel! He's had a revelation and wants to talk to people about it. But he's also available for comment box discussions and sparring/skill practice
He might especially want to talk to his bondmates, people who might have met said boyfriend when he showed up at the last fourth wall, and Thorne and her liminal family
also how is thorne supposed to know that finding the knife memory would also be giving her brother back the memory of the first time he and his pre-moebius boyfriend said they loved each other
i think the previous ones with thace in that she'd found were early ones where they were still just friends and thace was teaching him to Fight Like A Galra
like he did want to know where he got the muscle memory for what he did at the end of moebius, so i'm sure he'd gotten the Death By Neck portion of Fighting Lessons, which means he was well aware that there'd been UST between them
Thace probably recovered a few like that on his own. Them doing stuff together on jaunts (because initially he was focused on recovering jaunt memories) and a solid "I trust this person" ...which for Thace doesn't definitely mean "boyfriend" ...could be someone who'd become like a brother-blade!
he was thinking Thorne would question it, if he said it like that, and he could say something ridiculous and then go "actually, the first part was true"
no wonder he fell out of ambit when the fourth wall endedyeah that would be an intense memory to recover. especially if he didn't know already that they were dating