But Glenn came to serve Queen Leene at some point after that. Why? It's never brought up in canon, but I think...
Actually, it
is brought up in canon:
GLENN: C, Cyrus!
CYRUS: R...run...Glenn...
The Queen.
Take care...of...Leene...
.........
Glenn felt compelled, and was even ordered (or begged, I suppose) to return and take care of her. By his best friend. Through his
dying wish. Now, Glenn already cared about the queen - as did Cyrus - but this entreaty from Cyrus would have driven him to rise above his self-loathing, his desire to retreat, for the sake of his friend, in addition to the standard sense of duty.
But let's pretend that dialogue wasn't there, and go back to your scenario for a moment:
Leene somehow comes to meet Glenn in exile and takes great pity on him. Glenn is moved by her compassion and vows to serve her. | And so the seeds of love are sown.
The "|" is where some link seems to be missing, to me. What you described up to that point sounds like a form of loyalty, like a deep friendship. The kind that exists between Schala and Janus, between Glenn and Cyrus, between Schala and Melchior, between Robo and Lucca. I actually happen to think that the loyal love of a true friendship is the strongest there is, because it has no ulterior motives.
But regardless, the game script does contain the explanation for Glenn's immediate return, even in his humiliating frog form. And overall, the script contains much to support the shame/pity relationship (and the deep affection of friendship, like the other duos mentioned above), and not really anything to suggest romantic feelings. Just according to the in-game dialogue.
This scenario is the most compelling to me because Glenn is made to look too weak otherwise.
I honestly don't see Glenn's actions and feelings over Cyrus to be weak at all. Not weak, but in deep pain. If you had a best friend, and he had been for your entire life, since childhood, and then he was taken from you - while he was trying to protect
you... That's one soul-crushing blow - how do you know it wouldn't break you, shake you to the core? This is what I imagine it felt like to Glenn.
Truth is, I see something akin to that in pretty much all CT main characters. Lucca was traumatized by her mother's accident (it drove all her future scientific efforts); and the townspeople view her as a scientific joke, always failing - an outsider. Marle is extremely lonely - a passionate and adventurous soul, trapped within walls of royalty, with no one else like her in her life; viewed as a spoiled brat, when she really isn't. Robo has nothing - no place in the world, abandoned by his kind, not even human. Ayla is strong, to be sure. But she, too, is an outsider. Because she feels it's up to her to fight every battle for her people, she's alone it her mentality - no one else shares that burden. Magus was stranded in the middle ages as a boy, after losing his closest human bond. He was all alone physically and emotionally.
That was their life before the game started. A group of very flawed, very solitary, very independent people - who came together and became complete, vindicated, and co-dependent. And just...friends. That's what I love about the story. The world's outcasts, from every era, but put them together and they become true heroes, even happy. It reminds me of the characters from "Lost" and the kids in Dragon Army in the book "Ender's Game," in that respect.
Anyway, I don't see Glenn as weak - only broken, until he is put back together.