Back when I had a straight best friend in high school, I weirdly was only attracted to him for like 2 days at some random place in the middle of our friendship. He was hot, he had chicks crawling all over him, but for some reason I always thought of him as a brother and a friend. He kissed me once but it was a joke and I took it as such... our friendship really was genuine and precious to me.
I think the closeness and familiarity we shared was actually what diffused any sexual tension there might have been. I knew him too well and he me for there to be any "fantasy" about what might be possible. But that didn't stop his parents from asking if we were sleeping together lol.
I'd be horrified, just because I find my straight close friends to be hideous.
One straight friend had a sex dream about an other straight friend, woke up terrified and covered in sweat, and then immediately called that friend to tell him all about the freaky dream. Ya, they're close.