Tell me you're young without telling me you're young. Friendships are more than just meat space meetings. Children, moving countries, crazy work schedules are all reasons that can prevent you being in the physical presence o your friends. Does not seeing them for years at a time make them less friends? No, not to me.
There's a degree to how much you continue to engage with people once they've made that decision to leave though. Once someone's on the other side of the world, you're not keeping the friendship up by viewing their Instagram/Facebook posts, it's a totally one sided consumption unless you continue to speak to one another at least semi-regularly.