How long did you take to fall in love with your partner?

Hey Reddit, I would like to know how long it took for you to realize that you want to be with your current partner (or ex-partner). I'm asking because the guy i'm dating asked for exclusivity after two weeks. I don't have deeper feelings for him atm but i appreciate his friendship a lot. He is quite young (18, i'm 27) and says he had feelings for me beginning from the very first moment. He wants to brake off our friendship because i don't have the same feeling for him than he has for me. I would really like to stay friends with him but i'm afraid he won't be able to manage that kind of situation.. any tips?