Is it normal to have a new twist on a fetish?

Ive always been kind of a foot guy. But just giving foot massages and maybe kissing them but thats it. Im completely heterosexual and always have been. A very close friend of mine is a Trans-woman. Weve been friends about 2 years now but nothing more than that. Almost brother and sister like. I never knew her as a man. The other day we had some drinks at her place which we've done a million times before. We were watching videos online about porn stars and underneath it was a foot fetish video. She told me that she had heard from a mutual friend that i had one. I said no out of instinct i guess. But we dont lie to each other so i corrected my answer and told her that indeed i had a slight foot fetish. I dont remember too much of the conversation because of my adrenaline surging and thinking i was on tbe verge of a panic attack. She put her feet in my face and the next thing i know im masturbating whiles shes telling me to sniff her feet. This happened about a week ago. Still ive been to her house 5 days in a row now. Same thing each time. I get myself off while sniffing and licking her feet. Once its over, its like someone flips a seitch and we return to as if nothing ever happened and were baxk acting like brother and sister bestfriends again. I dont see any of this stopping any time soon. I get that it maybve weird but its not really to me. Im actually wondering if there may be something i dont know about my sexuality seeing as how she still has male genitalia. It feels innocent but am i missing something?