He ignores her in front of me, why?

This was some time ago but still bothers me a bit when I think about it.. So here we go: My boyfriend and I, together for a few years at the time, walk into a store. I notice a female customer but don't I don't pay attention. On my way out, my boyfriend tells me it's one of his exes. I ask him why he ignored her, why he didn't say hello to her and why didn't he introduce her to me? He replies that he was uncomfortable doing so. Some time later, I notice that they had already been talking on social networks for a long time, long before having met her in the store. Why did he ignore her in front of me? thanks (Please be kind..)

He ignores her in front of me, why?
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