Why do some heroines retain keigo(敬語) with their lovers?

[疏疏.]

Why do some heroines continue using keigo (敬語) with their love interests even after entering a relationship or getting married?
For instance, the way 星野市香 (Hoshino Ichika) addresses 岡崎契 (Okazaki Kei) and 白石景之 (Shiraishi Kageyuki) in Collar×Malice.
It comes across as oddly distant. Is this rooted in cultural differences?
Also, are there any love interests who stick to keigo when speaking to the heroine most of the time?

 

[mentaik2]

I think it's partly a cultural thing, but also a character personality thing! In Japanese, continuing to use keigo doesn't necessarily mean someone feels emotionally distant from their partner. Sometimes it's simply a habit, especially if they've been speaking that way since they first met. Since Ichika is younger than all the LIs in Collar×Malice and is naturally pretty polite, I can see why she'd continue using it even after entering a relationship!

Gekkamaru from Nightshade is an example! He continues calling the FL, Enju, "Enju-sama" and speaking politely even after they become romantically involved. I think it's especially interesting because his formal way of speaking is so deeply ingrained in him due to his role as her protector!