SO & Old fling

My SO and I went to Walmart tonight because I had to return something. Well I was walking faster then him so I notice the girl that was working customer service cashier was this girl that used to like him and talk to him before we started dating. Well I just kept on walking but my SO stops and tells me oh I'm going to go look at something and walks away but I know he seen her I felt annoyed that he just leaves partially running from her. I return my item and go find him and asked so what was that about he said he didn't want her to say hi to him and she used to be annoying. But I just feel it was something more then that. Do you think it was or am I just being a girl and over thinking things??? It honestly just threw me off 😤😲😫