Despite the fanon(/fandom) jokes about Plo Koon and attachment, he actually does a very good job of letting go of Ahsoka. The advice he gives Anakin in the Trandosha arc – that he has prepared Ahsoka all he can for this situation, and there is nothing more he can do now, and that doesn’t mean he’s letting her down – is from his own experience.
He wanted her to be his Padawan. He expected her to be his Padawan.
He has a nickname for her (much like Anakin has ‘Snips’), and they share a greeting ritual from his homeworld. He judges Anakin’s teaching to Ahsoka, indicating in no uncertain terms he thinks the way he wants to teach her is better; “You have inherited many of your Master’s ways, including a… lack of subtlety.”
Even in the Trandosha arc itself – what Anakin describes as Ahsoka’s strength, Plo says can also be a weakness. Plo asks rhetorically if she’s a worthy apprentice, and Anakin says nobody has her kind of determination (which isn’t exactly a ‘yes’), and Plo says “Except you”. (“You have inherited many of your Master’s ways, including a… lack of subtlety.”)
Yet, when Ahsoka goes to him for help defying Anakin, he backs up Anakin’s decision, and he says “He is your Master.” He might not like that, but he respects it, and he expects Ahsoka to respect it as well.
Back to the room in the Temple when Ahsoka has been captured by the Trandoshan hunters. He says “If you have trained her well, she shall take care of herself”. If. It’s pretty clear he isn’t sure that Anakin has trained her well. You know the moment when Anakin demands to know why Obi-wan isn’t on edge, and Obi-wan responds that he’s better at hiding it? I’m pretty sure that’s what’s going on with Plo, in that moment.