He's MY little guy

When we pick Brother up from school he is usually playing with one or two other boys from his class. They give each other hugs good-bye (very boyish, almost violent hugs) and then we are on our way. Today Brother was playing with Sadie. Sadie is a girl. She is five (way older than my sweet little guy). Brother referred to Sadie as his girlfriend. Then, she got in on the hug action when it was time for Brother to go home. They hugged, then hugged again - then again. Instead of the boyish violent hugs, it was kind of giggly and sweet. After the third one I kind of yelled, "OK, THAT'S ENOUGH" in a high-pitched nervous voice. I suddenly wanted to tell this five year old girl to "LET GO OF MY LITTLE BOY!" And maybe give her a mean look to scare her away.