Love boy-mean boy

so ............there is some guy named Robert who lives to the house next to me. I knew him for about 6 years. But i didn't know him as a friend...I knew him as someone that went to my school. Since we were younger.....u to the 6th grade.......we hated each other. He thought i was annoying and i thought he was annoying to. But since this year, he has been acting strange. He is being nice, smiling with me, and we go into somewhat of a short conversation every so often. My older sister is also friends with hm. It sounds perfect, right? I like him, or at least that was what i thought. So he is nice to me when we are not in school, he tries to impress my sister and i. The thing is, there's a catch!!!!
When we go to school, he completely ignores me and is totally mean to me. On the bus he doesn't even talk t me. He tells me tat he hates me. So then i don't like him. What do you think i should do.....give hi a chance? Or not? and if yes....what should i do differently? Is he normal?