Tell them. There’s no use pretending to be friends with someone for three years while you secretly pine for them, hoping against hope that one day they’ll turn around and declare their undying love for you. It’s not going to happen. Because, to them, you’re a friend. This is precisely how you get these poor sods complaining all over the internet that they’ve been ‘friend zoned’. They’ve played at being a friend, and guess what, their friend thinks they’re a friend. Jesus!