There's a lot to say here, especially in the way of how this is the first time that they've so much as had an argument over Amartolosa. If her presence really bothers Toby so much, why hasn't the vampire said anything until now?

But the thought, true in some senses, is a cheap excuse. He knows that the only times Toby ever so much as brings up his feelings is when pushed to, or when he's reached a breaking point. It's part of what's made this work out for as long as it has-- that Toby will put up with it all without asserting himself. It's made things easy, and made it so difficult decisions or sacrifices didn't need to be made.

And he still doesn't want to make any of those sacrifices.

"I was trying to make it work for everyone," Dorian explains slowly, drawing in a breath to steady himself. "Because I didn't --I don't-- want to let either of you go."