I think it’s more than possible, because they know so much about each other and have probably been through a lot together. Speaking from personal experience, I don’t think there’s anything in particular to ‘do’ to move out of the friendship zone. For me, it was more like something just clicked one day and I saw that person differently. And perhaps that’s what needs to happen in both people — a realization that it’s rare to find someone who knows you so well, someone who understands you, someone who makes you feel complete.