Help to talk to my friend

Hello..I'm a teenage girl. I have this amazing guy as a friend. I met him last year at my workplace. He is really cute and funny and sweet. But being the shy girl that I am, I don't talk to him at all. We chat a lot, almost everyday, but talk face to face very rarely. I have been learning in a girls only school since 4th grade, and I find it hard to talk to boys normally. I might like my friend just a little bit, just a small crush. But he doesn't like that I don't talk to him. We have had fights over this issue many times and I've apologized many many times. Each time I have a shift with him I decide and resolve to talk to him, but whenever I meet him I'm always at a loss for words. I just don't understand what to talk about because I know him very well already, and as I already mentioned, we chat a lot. Now he's angry with me again because I didn't talk to him, and I'm feeling ashamed of apologizing again because it might be seeming like my apologies are fake and don't really mean anything, although I really feel sorry and want to talk to him. What do I do?? Please help!