Ill quote sam from another thread who actually summed it up well:
“Thus, since it’s a Lav which is part of the Issur Arayos, we Pasken that it’s Yeihareg V’al Ya’avor. I said I won’t debate what’s Derech Chibah or not, because Derech Chibah is inherently very subjective.”
we also see the mechaber says for a husband and wife certain things that are not derech chiba for starngers will be so for ones wife- regarding the eztba ketana mentioned in the gem. look it up inside.