I'm very attracted to my best friend's sister?

So my best friend's sister is three years older than me (I'm 23) & my best friend. She's very attractive, not because she's hot, but because she's very 'sophisticated': she is a very mature person, she has a very worldly view about things, she's traveled over the world like I have, experienced various cultures. I see myself moving to Africa very soon, & I've spent many years of my childhood in Asia & Africa. She's also lived in China for a couple of years as a part of her job. She's just not like other American girls, & that's what I find attractive about her. She's in a relationship though. I don't want to have sex with her, or be in a relationship with her, I just like spending time with her, because she's the type of person I love spending time with. I'm not gay, I'm straight. Is that weird on my part? What should I do?