I need advice about what to do with this guy..?

I like this guy, he work's with my mom and we have been flirting back and forth for about a month now. I began to get suspicious that he was into me when I asked him to go with me and my son to see the movie "Cars 2" since I know he has a son around my son's age and his reply was "Maybe" and anyway after that everything was still the same and we flirted back and forth and the movie thing wasn't mentioned again. Today my mom happened to be done work at the same time he had to be in work and me and my son always go and get my mom at work well he walked in with some girl and I heard her say to him before I walked up to him "Is she in here?" at first I thought maybe she wasnt with him and they just walked in at the same time but anyway when I told my son to say Hi to him I heard her laugh, I don't know what to think or if I'm reading to much into this. I don't know who the chick was my mom said she thinks he looked like her so she thinks it was his sister. I'm not sure it was his sister tho..My mom also told me a few weeks ago that he had told her he was single so I don't know what to think. My mom thinks I should act like nothing happened but idk if that's a good idea..if you were me would you act like the girl coming into work with him never happened?