why am i so obsessed with this guy??

i (18F) have been seeing a guy (23M) who i’m really into for the past month and a half. he’s so sweet, funny, gentle, and we just get along really well. he treats me better than anyone i’ve ever met. he’s also very good looking.
this is just background information to say i’m insanely attracted to him. like, FIXATED on this dude. i used to watch porn pretty regularly to get off but it doesn’t even work on me anymore. i can’t get off because the guy in the video isn’t him so i get grossed out. even reading porn stories is ruined for me if the guy says something he wouldn’t say. can’t listen to porn audios because it doesn’t sound like his voice. literally nothing works anymore and it frustrates me.
him and i haven’t even gone past second base yet but i think about him sexually pretty often. it’s not that i ALWAYS am wanting to have sex with him — i love his company and just talking to him. it’s just concerning to me that he’s the only person i can sexually desire anymore.
i’ve been in love before but i’ve never been so sexually obsessed with a person. in past relationships, i could watch porn, fantasize about other people, etc. i can’t do any of that with him — i literally only want him. it’s also weird to me because we haven’t even had sex. i thought this might be part of the reason, but i’ve dated other people for longer periods of time before having sex and didn’t feel like this at all. what is it? why is he the only person i find attractive?