My friend (16, M) loves to stare at my sister (18, F) any advice on how to navigate this and/or deal with it?

110 percent sure they like each other since he loves to stare at her especially when she is in shorts or in a dress or a skirt. She also loves the attention as well and even hugs him for a long ass time and kisses his cheek. They are a grade level apart and I have known him since elementary school. He asked me if it is fine to ask her out and I trust him. I am just nervous and they are already so affectionatea with one another. She will sit on his lap and cuddle and hold his hand at school.

My friend (16, M) loves to stare at my sister (18, F) any advice on how to navigate this and/or deal with it?
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