...the best relationships shouldn't need institutional hedges against infidelity and/or abandonment. But an awful lot of relationships worth fighting for do end up benefiting from being hedged around with institutional supports - because life is long, people are complicated, and you don't always know when you're starting out what you'll need to reach the end of the road together. Yes, relationships are about the two people involved far more than they're about anybody else. But that doesn't mean that they aren't also about the community, particularly when kids are involved. The private is central and essential, but it still spills over into the public; your relationship is about you and your partner, but it's also, inevitably, about your friends and neighbors as well.
Exactly. And the support of family and friends is critical to helping a relationship through good times and bad. Why it is good for a society to deny this to a small minority is beyond me.