Feelings change over time. The world and human relations aren't as simple as you're making them out to be. Normal people gradually grow accustomed to the idea of marriage, and feelings of wanting to be together permanently, after a significant period of time.
Most of your current friendships will probablly up going nowhere, in a few short years time you won't be speaking to most of them. You'll have some dramatic failings out with your friends, ending with someone getting hurt.
Does this make the friends you currently have, and the friendships you've had in the past pointless?
Relationships don't have to end with someone getting hurt. It can end peacefully, you can remain friends with a former partner.