Basic Trope: A commitment to pursuing an unconsummated relationship.
Straight: Alice loves Bob, although he is to marry Charlotte, but Alice is happy simply to show him some affection without going any further.
Exaggerated: Alice loves Bob, even though he is to marry another, and it is her greatest joy to love him from afar, without even letting him know her feelings.
Justified: Bob and Charlotte are the scions of powerful Feuding Families, and their Arranged Marriage has been the only thing preventing outright war since it was first planned. Bob's Unlucky Childhood Friend Alice has come to love him, and he her, but all concerned understand the necessity of the marriage and the danger of dishonoring it by adultery.
Inverted: Bob loves Alice, despite his being betrothed to another, and longs for her even while he is committed to the betrothed one.
Alice writes a flowery poem on the painful joy of love unattainable to Bob, and then she gives it to him, along with a request to take the relationship further...she wrote the poem simply to impress him with her skill as a poet and the depths of her feelings.
Bob actually learns of Alice's devotion to him, and seeing as how the Arranged Marriage is loveless and neither spouse pretends otherwise, the love stops being, well... "from afar".
Double Subverted: Same as above, but she is made to abandon her approaches by Bob's betrothed, and she will have to settle for fulfilling the trope straight.
Alice gets goo-goo eyes and talks nonsense whenever she sees Bob, who seems acutely embarassed by the whole thing. Charlotte just rolls her eyes.
The whole romance is treated like a modern high-school girl's Celeb Crush. Alice has an oil painting of Bob over her bed which she kisses every night...
Bob and Alice are devoted to the idea of Courtly Love, but sometimes they can't help themselves, and the series combines Will They or Won't They? with their internal moral struggle.
Alice and Bob's culture celebrates courtly love in songs and stories; while some people take this seriously, others are just as adulterous and hedonistic as you'd expect. Sometimes this is treated as a fact of life, other times as a betrayal of one's marriage vows... basically, people's sex lives are just as diverse as they are in real life.
Averted: There are no Courtly Love romances in the story.
Enforced: They're writing a chivalric romance.
Lampshaded: "Ah look, Bob is longing for Alice from afar...he probably thinks he's in some sort of chivalrous romance novel".
Invoked: "Ah, what cruelty from Cupid, who shot the arrow of desire at me, that I may long after the lovely Alice, betrothed to the feudal lord for the sake of her father's ambitions...hmm, I think I shall write a sonnet about it".
Alice makes her desire for a relationship known to the one she loves, even if it might be socially unacceptable or even dangerous for her to do so.
Discussed: "It's nice to finally meet you, Bob. So, how many courtiers do you have loving you from afar? I've brought a couple as members of my personal retinue".
Conversed: "I'm sure that kind of relationship existed when everyone was stuck in Arranged Marriages, but I'm skeptical about the idea that they weren't screwing around in secret".
Bob resolves to love Alice from afar, even though it is not impossible to consummate a relationship with her, because in doing so he is able to enjoy his tender, passionate feelings without any responsibility towards her, and also to more easily blind himself to any flaws she may have because he does not have to deal with them, thus selfishly falling in love with an idea rather than accepting the real Alice for what she may be.
Alternatively, it is simply that Bob is unable to let go of Alice, despite her unattainability, and thus his overtures are more like being a Stalker with a Crush.
Reconstructed: Bob concedes that his "love" for Alice may be unrealistic, but it fulfils a deep spiritual need that his loveless marriage of convenience doesn't. He thinks that if he were to throw all romanticism aside in favour of cynical pragmatism, he'd become an immoral person.
O, adore that fair and beauteous trope the angels call Courtly Love. But go there not, for it is unseemly that we mere mortals should despoil its pristine perfection...