How do i handle my boyfriend?

My boyfriend and I have been together for 9 months. He says he loves me, but im not sure if he truly does anymore. We are in high school and he lately has been texting other girls A LOT more. I also found out that he has been buying hershey candy bars for another girl in one of his cles and he has been going to his "best friend's" house and she and him have been hanging out at like midnight at her house. I told him this bothered me and yelled a little but he did not listen to me. He says they are just friends and nothing more, but as his girlfriend I automatically get jealous and a little protective of him. I just don't want him to cheat, which I am a little suspicious of right now. I want him to understand I'm extremely uncomfortable with him behaving this way with other girls but I don't know how to get him to listen because he makes up excuses for everything. When he does make excuses, I get pissed and yell and then we start fighting, which I hate doing but it seems as if it's been happening a lot more lately. I want him and I to be together but I need advice!