I'm gay for him but in the closet

I've known this guy for about 2 and a half years and we're pretty good friends. We're both in the drum line in our marching band which has us near each other almost the whole year. He's going to be a senior next school year and I'm going to be a sophomore. He's been giving some signs. Hanging around me a lot, rough housing with me a lot, and talking, trying to get me to laugh, and just (what I think is) flirting. I have just figured out I am gay and have told no one. I'm trying to keep it as secret for as long as possible so my mom doesn't find out because she's a homophobe and would send me to therapy if she ever found out. So Im really into this guy and I want to tell him but it's summer and I can't tell him in person so I want to text him and tell him over the phone and let him think about it over the summer. I need to know what I should tell him so that he knows I'm gay, he knows I like him, and To ask him not to tell anyone if he doesn't feel the same. Thank you.