For a while, Marshall and Robin were never especially close due to the fact that Marshall was scared that Robin would turn into a "mermaid" and he would fall for her. Robin went from the object of Ted's affections to his girlfriend and then his ex which shaped her relationship with Ted's loyal best friend, Marshall. At the same time, Robin was also Lily's best friend and, much the same way Marshall and Lily's relationship put a strain on Marshall and Ted (Duel Citizenship, The Duel), it would put a strain on Robin and Lily (Woooo!). Even so, they were close enough that Marshall would call up Robin crying when she was planning to move to Japan. (Intervention)