"I love you"

If someone tells you they love you and you don't think you're in love with them yet, what do you do? It hasn't happened yet but I feel it coming. My family says they can tell this guy is in love with me and I like him a lot but I'm not quite there. I think I may be one day, but not now. What do I tell him when it happens?? I don't want to hurt him but I wish he would slow down a little and let me catch my breath. We've been talking for like 5 months but it's just now getting serious and it seems to be happening really quickly all of a sudden. I like him a lot and I don't wanna ruin things with him by brushing off his feelings but I don't feel what he feels yet.