The Harvard Study of Adult Development may be the longest study of adult life that's ever been done. For 85 years, we've tracked the lives of 724 men, year after year, asking about their work, their home lives, their health, and of course asking all along the way without knowing how their life stories were going to turn out.  The clearest message that we get from this 85-year study is this: Good relationships keep us happier and healthier. Period.  We've learned three big lessons about relationships.

The first is that social connections are really good for us, and loneliness kills. It turns out that people who are more socially connected to family, to friends, to community, are happier, they're physically healthier, and they live longer than people who are less well connected. The experience of loneliness turns out to be toxic.  And the sad fact is that at any given time, more than one in five Americans will report that they're lonely.

The second big lesson that we learned is that it's not just the number of friends you have, and it's not whether or not you're in a committed relationship, but it's the quality of your close relationships that matters. It turns out that living in the midst of conflict is really bad for our health. High-conflict marriages, for example, without much affection, turn out to be very bad for our health, perhaps worse than getting divorced. And living in the midst of good, warm relationships is protective.

And the third big lesson that we learned about relationships and our health is that good relationships don't just protect our bodies, they protect our brains. It turns out that being in a securely attached relationship where people really feel they can count on the other person in times of need, those people's memories stay sharper longer.

Why is this so hard to get and so easy to ignore? Well, we're human. What we'd really like is a quick fix, something we can get that'll make our lives good and keep them that way. Relationships are messy and they're complicated and the hard work of tending to family and friends, it's not sexy or glamorous. It's also lifelong. It never ends.