How do you know if someone likes you back?

I like my boss and sometime I feel as if he likes me or if I'm attracted to him. He sometimes does this sexy ass face to me while he's smiling but I don't want to think wrong. I just think he's smiling me with generosity but idk.. he's very attentive with me but he prob is attentive to everyone else too. I had a dream about my boss and I dating and that my co workers had told me be careful with him because he has dated every one of them. Should I be aware of sometime or Am I just over thinking??