Usually it's the woman that bears the brunt of keeping the family together, taking care of the kids in nonmonetary(and sometimes pati na monetary) terms, managing the relationships within the family, etc. And kung sakaling maghiwalay, sa napansin ko usually sa nanay napupunta ung burden of raising the kids. The man is supposed to pay alimony and such...but enforcement of laws always was weak here in these islands. This is just my impression though.
Live-in -- assuming it doesn't involve sleeping around -- does make sense to me, if only to test if the attraction you feel for each other is purely lust/spur of the moment as opposed to something more meaningful.
The romantic side of me actually admires unmarried couples who stay together: they don't stay together because they are bound by marital laws, but by love(naks)...
...but if you throw in kids in the equation, it gets complicated: baka tinitiis na lang ang isa't isa for their sake. Ganito ata ung case where couples that have been together for ages suddenly file for divorce/annulment. Siguro sa isip nila malaki na ung kids ang mas nakakaintindi na.