Why do people who dislike me act nice to me after talking to their crush?

There is this married guy at work that is friendly with everyone but me. I feel like he doesn’t respect me and considers me beneath him since he forgets his manners around me only, acts aloof and is very short with me while being extremely chatty with everyone else. However I noticed that on days where he gets to talk to a certain female colleague he acts super nice to me, his eyes would light up when he would see me, he would go out of his way to greet me, smile at me or offer to help me. With the female colleague it’s the same. While she would sneer at me on normal days she would smile at me when she gets to talk to him.

1. Why does he not respect me? He and this female colleague are the only people at work that openly dislike me

2. Why does this woman (he probably sleeps with) have such an impact on his behavior towards me (a person he obviously dislikes)

Why do people who dislike me act nice to me after talking to their crush?
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