Aria, I just wanted to say that you did a good thing, making a clean break from Peter. It must have been tough to let go of an old friend, but Peter is no longer the friend you had, and will not be able to be that friend to you ever again until he has a chance to get over you. You did him a kindness by making things very clear, so that he cannot delude himself any longer.
Reading this story made me think of two problems I have. The first is, I feel like especially as a woman, I was brought up with the idea that saying "no" is rude to do, but if you have to say no, it's necessary to soften it somehow, to spare the other person's feelings. I have a much stronger spine now than I did when I was in my teens and twenties, but back then if a guy I had no interest in asked me out, I would have been more likely to respond with something like, "I can't this weekend, sorry, I have to go help my grandmother. Maybe another time," to mitigate the blow to his ego. After all, he might think I was a female dog if I just said no with no explanation (gasp, the horror)! Of course, as I've since found out, these open-ended nos are bad news because while some guys pick up on the clues when a girl turns them down 3-4 times in a row, there are plenty of guys that do not. I bring it up because had I been in Aria's situation back when I was younger, I could have easily seen myself saying something along the lines of, "Peter, I think you're a great guy, and you'll be a great boyfriend for some lucky girl! I'm really flattered, but I'm not looking for a relationship right now." I'd be thinking, "Whew, I let him down easy. I hope he's not mad at me and that we can still be friends." He'd be thinking, "She thinks I'm great, and she's flattered?! She says no, but if I keep asking, eventually she'll say yes."
Which leads me to problem #2: I feel like the media has a hand in influencing people of both genders to think that if they just persist long enough, the unattainable person of their dreams will see all of their charms and fall madly in love with them, as long as they are willing to wait it out and keep trying. It's so romantic! And it can make for a sweepingly epic book, or movie... but in real life? It's creepy, unhealthy, and borders on harassment. The ironic thing is, many books and films popular with women have this exact trope, and men assume that's what women are looking for, a suitor that won't give up and won't take no for an answer. See: Twilight, Say Anything..., Pride and Prejudice, etc. Double the whammy when the movie/book, etc. involves friends becoming lovers. Aria, Peter was probably hoping he'd be the Harry to your Sally.
I don't think you did anything wrong, and I'm glad that Peter finally got a dose of reality. If a situation likes this ever comes up again, you'll know how to handle it.