Why can't guys & ladies just be friends? Also is it a slap in the face when you correct a guy?

Yes, I know that guys and girls can be friends but there is also the thing when it was your attraction to the other person that was the cause of a development of a relationship. So where do you draw the line of attraction? I highly doubt that people mark their lines at the same point, most of the time there's one person in the relationship that is more attracted to the other and it sucks. I've seen and experienced friendships turn into something more but I thought I was done with the guy friend falling for the girl. To me, I guess you can say it's sweet. But, it's like dude, why f*ck up something that is already good like I thought everything was fine until feelings were brought up. I might be insensitive right now but I just hate losing friends and last time I've been through this, I lost that friend. That's probably why I'm here asking for help. I always thought I was... what do some people say "a guy's girl", you know a girl that was mostly friends with mainly guys. Well, here's the problem: people keep saying I'm this guys girlfriend and like on a post they were like get your girlfriend and he can see the post of course but is it a slap in the face if I say I'm not his girlfriend. I can ignore it but its bound to come up again and I could stop commenting but it doesn't mean that it'll go away. I know his feelings for me but I can't return those same feelings. He's close to all of my other guy friends and I bet they know too, it's just UGGHHH!!! I don't know what to say. I don't wanna hurt him but if I need to stop talking to him then fine, whatever I guess if it's best. Can't believe this is happening again. Any advice will be great. Also if anyone knows how to stop a guy from falling for you (I guess you can say) that would be great. Please & Thank You.