as one has had first hand experience of having many many friends and quite a few close family members in 'live in' relationship, let me give my 2 cents worth here.
first of all, i think it is a mind set. of two people, in love, and to move to the next stage of relationship. in this framework, no one else matters ie not the relatives. not the society. not the norms. not the morals. these are not taken into consideration, or are considered irrelevant.
btw there is no having multiple partners and such. it only reveals a level of ignorance. if you are having multiple partners, you live alone, so that you have the privacy and convenience to have such a lifestyle..
a living together is an arrangement. everything about running a household - starting from paying the rent, food - purchase, cooking cleanup, maintaing the household, laundry, paying all the utility bills and yes, sharing the bedroom. i mentioned the bedroom, as last in sequence, because, had the lovers interested in sex only, it is easier for them to meet in each other's place, do their thing, and part.
but 'living together' is a commitment, to a relationship, with the hope of forming a nuclear family. it is not quite marriage, as it is devoid of rituals and legalities (though in canada, if you live together for 3 years, you are considered 'married' in the eyes of the law).
'living together' takes the glamour away from the romance, and infuses in it, a strong dose of reality. the dolled up female who attracts you, in the morning, sans makeup, and in her moods, is a different person to get used to. the man comes to know the woman, on a more intimate level, ie her personal cycles, moods, preferences and above all, the REAL her. there are not many warts that you can hide when you are exposed to a person day in and day out.
the same goes for the man. the girls gets to see the guy's stubble in the morning, the bad morning breath, the smelly farts, the mess he leaves behind after he takes a shower, and umpteen other aspects of young men, which disgusts women.
so, dear sangom, Brahmanyan, et al, 'living together' is no bed of roses. it is a preclude to marriage, but more, it is a rehearsal for life together. it is done, normally, after much thought and evaluation, particularly from the girl, because usually she has most to lose, from way of mental heartbreak, if things dont work out good.
it is also a sobering lesson to the guy. what real life and marriage is all about, enough to scare some boys, to call it quits. and that happens. but most work it through, and nowadays, formal marriage in many many instances in the west, take place only after a somewhat extended period of 'living together'.
i repeat once again, there is no extra indulge in carnality or immorality here, unless you consider the concept of setting up a household between a man & woman, without the marriage papers itself is a immoral.
ok let us all, get off our rocking horses of wild imaginations, and look upon this as an urban phenomenon, world wide. whether we like it or not, is another story.
a colleague of mine, lady, when she was now in her 40s, in early twenties, wanted to move in with her boyfriend. both whites. the girl's mother said NO. a few years ago, the mother was widowed, and a year ago, she found a man. they wanted to move together, and the girl, had her sweet revenge. she told her mother NO. get married first if you want to shack up with this guy
usually here no parent objects. they after all know the girl, or the boy concerned, and it would have been a few years, if not months, before these decide on setting up a household together. usually, before marriage, and sometimes, the marriage itself is dispensed with - due to finance or 'cannot be bothered with it' attitude. legally, these are man and wife after 3 years of cohabitation - for legal, pension, divorce, child support and all such purposes.
questions?