If you know a chick was attracted to you, and you guys never worked out or got in a relationship for reasons out of your control (bad timing she just got out of a relationship, or she caught you talking to another girl and assumed you weren't interested etc) I don't see why it would be a blow to your ego to remain friends with her while she continues to date other guys. Why take it personally if she liked you at some point?
I think guys blow the friend zone thing way out of proportion, I've banged a lot of chicks who I thought I was in the friend zone with. When a girl cheats on her boyfriend who do you think she runs to? One of her friends lol. If a girl has ever gotten physical with you and uses the word friend with you that's how she convinces herself she's not a bad person for leading you on, while she's really keeping you around as a potential side nigga. Give it a few months and wait for that midnight phone call a few months down the line lol