My cat has a favorite guest and she isn't subtle about it

Whenever friends come over, my cat is polite but distant.Except for one person.The moment he walks through the door, she starts purring before he's even taken his shoes off.She follows him everywhere.She sits beside him.She ignores everyone else completely.I've known this cat for four years.He's known her for maybe six visits.Apparently I've been replaced, and she doesn't even feel guilty about it.