Most Helpful Guy
He's being possessive and he thinks that his persistence is displaying the seriousness of his feelings for you. But its actually just freaking you out and making him look like a joke.
Forget him, ignore him, move on. He will stop once he gets the message. Plus, you should tell one or two people you are really close to so that they aware. Always good to be safe.
Most Helpful Girl
Yeah he is bordering stalker and can't get over it. I really would keep it casual as you have been doing. He wants a reaction from you. Eventually he will get it but please do not give him the attention he is clearly wantig