Studies about romantic relationships, which marriages supposedly are, never seem able to capture the complexities of chemistry, compatability, and partnering.
Sexual issues, financial issues, disagreements, emotional issues and frailties, etc etc all beset the basically unnatural notion of lifetime monogamous bonding. In Western cultures, committment is important cement, but how often is it, really?
Good friendships can easily last a lifetime, thank God. That's partly because you do not live with them and have to deal with their flaws every day. Friendships are essential in life, I believe. No one partner can meet all of our relational wants, supports, comraderie, and enjoyments.
A relationship study: A landmark study shows what makes a successful relationship