GUYS WHAT DOES THIS MEAN!!!? BOYS PERSPECTIVE PLEASE.?

So, my sisters husbands friend saw me on facebook and pretty much requested me long time ago. My sister and brother in law are really good friends with him. So like I said he barley started talking to me like last week. He has only seen me on facebook. He has never seen me in person. He was telling my sister about me, then he asked for my number on facebook. Then texted me. Getting to know me. He always usually text me. Telling me about his my day was etc. That was last week. Then yesterday my sister told that he likes me. I found kinda bizzare because he barely knows me. He texted my sister saying he's met a beautiful girl. (Me) and that he has forgotten everyone else ever since he met me. He is posting things on his facebook saying that he can't stop thinking about me. Someone commented on his status saying "who are you talking about?" And he wrote my name. He was talking about me. I haven't even met him in person. Never have talked with him in person only text. I don't have revealing pics on my facebook. So he can't a pervert. But I don't know. Why would a guy act likes this? I mean he seems really nice though! But what does all this mean? Can a guy really like a girl he's never really met in person? What does this mean boys? By the way he's 19 im 18. Help!