[ Already posted this in /r/gay but I felt like it fit here. ]

So i'm going to be 18 in about 20 days [a little disclaimer on the age] I have strong feelings for my straight, older best friend and I don't know why, I just do. There is an attraction there because I'm attracted to chubby adorable guys but that's not what I primarily feel for him. I want to pursue something other than a friendship because I really like him and I feel that something romantic could develop between us. The problem is, I don't think he knows I'm gay and I don't know his views on LGBT. He is a really nice, kind, and welcoming person but I haven't brought up the subject to him. I'm having a 18th birthday party with my family and some friends and then after, i'm seeing a movie with just him and my other best friend and i'm planning to pull him aside privately at the theater and come out and tell him everything. The problem is, he's a close family friend and I don't want to ruin our friendship and make the dynamic awkward. He lives a distance away so I don't see him often but when he is in town I hang out with him all of the time. I'm getting nervous just writing this help? I don't want to move on from him, my best case scenario would finally being able to kiss him after thinking about it for so long. I'm a lost cause, find me so I don't go insane over it. TL;DR: I have strong feelings for my older best friend but he doesn't know i'm gay, i'm planning to tell him everything but I don't want to ruin the friendship. Update: I'm planning on telling him by pretending I'm talking about another person and asking for his advice on what I should do and in the end revealing that he is who i'm talking about.