And in almost any given culture, there is some kind of taboo or stigma about sex and sexuality, which is a key and complex component in relationships. The maturity to which a culture as a whole views sex and sexuality (and relationships as a whole) will affect how it is depicted by writers.
I was thinking of how hard that must make it for developers of RPGs where relationships can play a huge deal. Having to appeal to the whims of japanese or american gamers while observing tact must be difficult.
Speaking of games exhibiting adult relationships whenever I suggest Mass Effect to a friend I always mention how the acting and storytelling is more entertaining and believable than the new star wars movies.