I feel as though Dylan equated Purity in the sense of being genuine and absolute of character. Being authentic and true of one’s nature and spirit.  Uneffected nor easily swayed or influenced by others as part of the populace, the majority of the zombies imitating one another and relying on one another’s approval as part of the existing in The System here on the earth. A something or someone that/who is untouched and not tainted by the mass influence. A girl that Dylan equated with Purity meant that he could see her genuine spirit – she presented real – simply, wholly, purely who she was and he found that attractive. What you see is what you get.  No fakery. No Facade – they are presenting honestly in the world as they truly are.  Perfect as is no physical trappings by status clothing or illusions to enhance. She is pure in her purity.   I feel as though part of the reason Dylan was so jealous over Zack’s good fortune with Devon is because he felt Zack truly lucked out with a girl that had purity of nature and spirit.  She was a real woman and she cared about her boyfriend genuinely. She cared about people..and she cared for Dylan and wanted to befriend him. Purity was something Dylan knew innately once he saw it radiate from someone and experienced it of their nature.  You are either someone that had it.. or you didn’t.  I don’t think Dylan equated purity in relation to girls in the traditional sense of whether they were virgins or not.  Although, I think in his mind, sexuality expressed in connection with love as the higher ideal and inspiration would be closer to the spectrum of purity than the act of fucking simply because you can and your body wants to – for the base lust and perverted desires of the ‘human self’.  Humanity, and the pit falls of re-acting as part of this illusion of an existence, is what Dylan perceives as an Achilles Heel that holds us back from being who we truly are as part of the Everything state of being.