How do I let him know I'm interested? (Please Please Help I know its a lot to read but I'm really confused and need help so please read and give an answer if あなた can.)

So I am a senior in high school and I know this may be hard to believe but I have never had a boyfriend. I've had the opportunity just never 発言しました yes. So there is this guy at that I have been フレンズ with since freshmen but he has become one of my best guy フレンズ in the end of sophomore and through junior year. I liked him a little in freshmen 年 and the beginning of sophomore year. None of my フレンズ no one at school knows this though because I am pretty closed off. At the beginning of sophomore 年 I and the whole school found out that he liked me. Since he liked me in sophomore 年 he has liked me on and off. In the 秒 semester of junior 年 he became really into wanting a physical relationship. He would ask me to sleep with him so it would be just purely physical cause he didn't want a girlfriend and he 発言しました it was perfect cause I didn't want a boyfriend. But I 発言しました no. This is where our relationship became a lot about me rejecting him but him just coming back and asking again. He has tried with going out with other girls but he always comes back to me. And now it has transformed to him not just asking me to sleep with him but also just to go out with him. But I still reject him I have thought about saying yes but I think I was scared plus I have rejected him so much it would seem odd to say yes. But on friday him and I and a big group of other フレンズ went to an event a theme park and he was saying to that I was his 日付 but I was taking it as just his usual thing but all night he would be holding my hand and had his arm around me and was 芝居 like we were going out. It made me realize that I might actually want a relationship with him but I think that he may have only been doing that to look like he had a girlfriend at the park. And I am terrified of saying something and making a fool out of my self. I never tell anyone things like this. What should I do please help I really need it.