Why do men have higher boundaries for certain women?

By distance I mean mostly physical distance. They don't shake hands with them, sit beside them nor even stand beside them. The conversations are usually extremely formal. I have a friend and if random men ask us directions or something, it's never her they talk to. Yesterday I noticed that the very chatty guy from the class had to sit beside her but he kept one empty seat between them. She's nice. So I'm very curious, why is it like this?

Why do men have higher boundaries for certain women?
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