Crushing confussion

Hi So, there's this guy at school that has been giving me a "crushy" feeling, like weird crushing. He's one of those good looking guys that are not that smart but get they're way through. I'm tomboy-ish: small boobs, tall, shinny and athletic... It all started when we were assigned a health class project about pregnancy and birth; it was a group: him, two people and me. I didn't talk to him that much because he had been a jerk/rude to me before but I spoke to him because I don't hold grudges and he is the best friend of one of my guy bffs, who was my latest crush... Anyway, we had to spend time together, although we only worked on the project in class. I was the one writing everything on the laptop so he had to spell everything that was going on our project. I was kind to him and we shared this moment when he spoke to me like we have known each other for more that 3 years and were super close. After that, our last day of school, I took my little guitar and asked everyone of my friends to sign it... He signed his name___ Have no idea why he did that... Then, he kept asking me for my Sharpies so he could sign other peoples stuff... Later, he began making an "S" on my arm with a Sharpie... A couple of minutes later, he did it again... The day after we had our Goofy Games day and I helped him roll up his sleeves to put on sunscreen... Don't know if I'm misinterpreting but I think there is something happening there. Please help me understand what's happening...