How I Met Your Mother Episode 5.07 The Rough Patch

Barney and Robin begin to let themselves go as they get into a relationship rut. When Barney donates his porn collection to Ted, sending a message to Ted, Lilly and Marshall that he's not the same person anymore, the group conspires to break Barney and Robin up. Ted, Lilly and Marshall set up a stake out in a station wagon following the pair. They try to break them up by forcing the issue of commitment and having an engagement ring appear in a glass while Robin and Barney are having dinner but inadvertently cause the two to apathetically agree to marriage. In another attempt, Ted, Lilly and Marshall realize their orchestrated attempts using Robin and Barney's top five fights of all time are unnecessary and they let the relationship take its course. Robin and Barney realize they miss being who they were before they became a couple and break up.