Zach knew T had interacted with - met - knew on some level the man Rosier had been getting together with. Barty Crouch, head of the MLE, very public and sexual gay man. Death Eater. Shagged up with Rosier. Bit crazy. Shagged with Rosier publicly in the hospital wing. That was the summary of what Zach knew. But given the man got along well with Rosier, Zach didn't think he was going to be Zach's brand of crazy. No, T was Zach's brand of crazy.
"What's Crouch's kind of crazy?" Zach asked, in case it wasn't just what he knew. He paid attention to loads, but Zach rarely if ever assumed to know everything.
Trace was becoming more okay with the polyamorous aspect, which made Zach happy. He still wasn't looking to try to make it happen any time soon or anything. But when it did, it was definitely better if she were already okay with it. Who knew what the bloke would think.