People need to stop getting married, or at least not so early. Marriage is a very intensive (and rewarding) commitment that I think most modern people cannot make. Instead, foster relationships that matter for as long as they matter.
I was in a serious relationship from 19-25. These things end because people change a lot in those years. We both graduated and went in different directions. Which I think is perfectly fine. Relationships will change. You can absolutely start new ones. Join pretty much any club that meets in person. Commit time to those who enrich your life, cut loose those who harm it.