Is he cheating or am I overreacting?

My boyfriend and I just got into a huge fight. Earlier tonight he was adamant that we watch a video about the phone he's getting before getting something to eat. I finally caved in and let him. Just as he starts the video he gets a text from a girl named Rebecca. I asked him who she was (not even accusing him of anything or being mean), and he just says " oh who? You mean her? Rebecca?" I said yea. He said " oh she just some girl who sits next to in class, and she's probably just asking me a question about the homework." I said oh okay. Then he grabs his cup and says "I'm gonna go fill this up with water" he grabbed it and turned his computer off and left. So the night goes on and it just seemed odd to me. Fast forward to 10 minutes ago while he was taking me home. I asked him who the girl was? ( I'd honestly forgotten her name, as I didn't find that important). He was just like Oh my god she's just a girl in my class! I asked him why she was texting him and why he didn't respond. I thought it was odd he didn't respond because normally when his classmates text him about projects or homework he texts them asap even when I'm around him. He ignored the questions and started yelling about how unimportant and stupid it was for me to ask him, and he just seemed to be really defensive, and he was like " god what do you think happened? Do you think I walked out of the room and fucked her and made her leave as I came back up to my room? Jesus! It's like you don't even trust me!" Do you think he could be cheating or am I overreacting?