i don't get why he does this to me

I don't get why he plays me like a puppet. I'm not some toy that can be played with. I'm human i have feelings like any other person. He plays me like im some kind of puppet that he can come back to whenever he wants. Everyday i deal with him flirting with me and then going to the next girl flirting with her. He flirts right in front of me everyday. He acts like he cares about me so much but then he turns around and flirts with my best friend. He flirts with my best friend everyday right after he flirts with me. I never question him or talk to him about it because I don't want to lose him as a friend or any chance I have with him in the future.