Ultraman

Since men are from Mars and women are from Jupiter (or the other way round), it's very common they have different needs in a relationship/marriage.
Say "sense of security", women might feel "lack of security" for some reasons, but to men they usually don't have this abstract term in their dictionary and so probably they have no idea what it is and how to comfort their women. Therefore, communication by open discussion/sharing and acceptance is very important.

On the other hand, usually men would have a stronger "sense of responsibility" than women. Generally, they have stronger sense to "take care of their women" in mind. And plus when men are more rational (not all men at all times), they don't see big problem in a relationship (unless a "3rd party" is involved).

Women could be rational and/or irrational. For example, a woman decides to leave her man because no matter how hard he's been trying to do, she can't feel the love of him, her decision of leaving him is irrational. A woman can't bear her man being layoff for years but still lazy to look for a new job and choose to leave him, this is rational.

Ultraman

I also think 同居 could be a very good "pre-wedding" progress for serious couples to try out whether they can really work together before getting married. However, they have to face some possible consequents such as, object by their parents (bigger change on the gal's side); in case they can't work out, then should they keep the progress to live with another potential partner over and over again until success? Then other people (their families, relatives and friends...) might think they're just too open minded to live with someone easily.

If your parents, brothers and/or sisters have different personality, different interest, different taste of food, different habit ..... to you, or even make you angry sometimes, but you know they deeply love you inside their hearts, they also try to cheer you and care you whenever you need..., would you be that mean and picky to them and choose to hate them or even to move out? I also agree, if you can treat your serious other half as one of your family member, chance of working out would be a lot greater.