What am I supposed to do? ?

There is this guy who was my science partner for a project in science last year. I hated him last year and this year we both tease each other and like play fight and stuff. And this year I wanted to be friends and it was so much fun to fun fight with him so I kinda liked him. And this year this girl said we should be together and she said whenever I say his name i blush. So I blush and he smiles and all these girls are like knocking me down asking me if I like him. And they say he likes me even more than I like him. The whole cl knows us to be like rivals bigger than VT and UVA. So I run away and I am frustrated. Then he comes up to me and asks if we can talk. He says they were right and he does like me and it is ok if I don't like him. I told him I did and we decided to keep on pretending we hate each other. So we told each other to not tell anyone. No parents no nobody. So my heart is beating and I can't stop thinking about him. I feel like I am going to have a heart attack. I had to lie to my mom cause she almost figured me out and I am so confused about everything. Should i break up with him or not? If not, what should I do? I am only in 5th grade. I know it is young but lots of people in my grade are boyfriend and girlfriend. I am so confused and sad in some way. Help please!