While they are hopelessly in love from the first episode, Lily Aldrin (Alyson Hannigan) and Marshall Eriksen's (Jason Segel) relationship continues to evolve throughout How I Met Your Mother. Lily and Marshall meet in their freshman year of college, get married in their 20s, and have three kids in their 30s. While they both have difficult jobs and struggle with fully committing to the relationship at different points, they also help each other find personal fulfillment.
https://screenrant.com/how-i-met-your-mother-lily-marshall-relationship-episodes/