We're at the risk of entering Schrödinger's cat territory here with respect to millennials and relationships. They have fewer relationships, they enter into fewer marriages, and they go on fewer holidays. Do they even get together at all? Apparently so, and when they do so, they tend to mate for life. Millennials get divorced less than older generations do - and that's not just because they marry less.
As a percentage, a millennial couple is less likely to get divorced than a couple over 45. This is a slightly misleading statistic because younger couples have had less time to split up, but the percentage of married couples who have divorced by age 35 is lower now than it was ten years ago. Perhaps because millennials wait longer to settle down with a partner, they're more likely to get it right first time.