Obsessed with friend’s feet…how to approach

Hey. I have a friend, who’s about my age. Have known him for pretty much all my life and I personally think he has the best looking feet I’ve ever seen. They are so soft, I’ve tickled them once or twice as a joke and it really made him laugh! Probably some of the most ticklish soles ever. I barely touched them with one finger. Wish there was a way to continue this…I don’t think he’s into that kind of thing. He is bisexual. He’s always barefoot around us at sleepovers and I’d like to think he’s doing it purposely but…what if he’s not? Weird situation but all I want to do is tickle torture his feet. But I don’t want to lose him as a friend.