"Theseus was disappointed you couldn't come to dinner. And the other nights we've asked you."
"He's your brother, Newt. He likes spending time with you. And so do i."
Friendly reminder that:
Theseus and Leta (Along with Bunty) were the only one who attend Newt's book launch to support him.
Theseus and Leta had asked Newt to come for dinner multiple times. Possibly waiting for him until their dinner's got cold in a hope Newt would come and spends time with them.
Implied in FB1, Theseus wrote a letter to Newt, wishing him well 'whatever beastly quests he's undertaking'. It's a small moment, but at least it shows he still wants to keep in touch.
Theseus made Newt his best man for his and Leta's wedding
Among the Scamander family, Theseus is the only one who cares a lot about Newt (at least, that's how we see it so far), along with his fiancee, Leta, who was also Newt's close friend since they were in Hogwarts. The relationship between them may be complicated, but it doesn't mean it's not genuine.
