AITA for being aroused by a female friend?

I(19m) only masturbate to porn, under the assumption that porn stars are okay with people masturbating to them. I have found girls I meet in real life to be pretty, of course. Past and present classmates. Some are very beautiful, and I’ve had crushes, but I haven’t actually looked at any of them in a sexual way because there’s no knowing if they would be okay with it. I never masturbated to people who aren’t porn stars since I don’t know if they would be fine with that. Never got an erection because them.

But then I met my friend ‘Riley’(18f). She is exactly my type. She is kind, caring and funny, and she is slightly muscular from sports. Everything about her put together just hits different.

For the first time in my life, I sat next to a girl, looked at her and got an erection. I’ve had random erections before, of course. I am already 19. I have gotten erections at awkward moments several times over the years. But it’s the first time a particular girl I meet in real life turned me on. And she wasn’t even wearing revealing clothes! Just her sports wear.

So I covered my crotch with a book and hurriedly fled. You know, like a coward.

I ran off and I foolishly told my best friend(19m) who proceeded to tell her why I ran. When she talked to me, I apologized. I told her it was my fault for not controlling my thoughts/feelings. She said that it’s okay, it’s a natural reaction and I don’t have to feel bad about it. But it’s still eating me up inside. I don’t feel bad getting hard for and jerking to porn stars since that’s the reason they shoot those videos.

But I objectified my friend and that’s different and it’s really unsettling. She said I’m not a creep for being turned on by her but I still feel guilty.

UPDATE : I sent a message to her, asking if she’d like to go to the cinema. Fortunately she said yes.