See, I agree that Ashe and Zoey's first time is considered a fling, because it is. But no other relationship would have had that tenor. It either would have been more serious, or would have been tragic (or fucked up, or otherwise tainted). I could see Fiona and Ashe's relationship surviving them being Ashe's first hookup, but only after a lot of turmoil and hand-wringing. No one else that had an emotional bond with Ashe would have been better. You could swap in the drug dealer chick fine, but then it's just another random to get Ashe past being a virgin. Fiona, Rachel, Delilah, Mom, Kate, even any of the girls at the sorority would have been more emotionally charged and plot disruptive choices. The only way to avoid major ramifications would be to ignore them, creating odd character behaviours and worsening the quality of writing.
Ashe is still ready (at least with some of the options) to dive head first into a relationship with Fiona. Only the distance she has from her previous hangups seem to let her grudgingly accept that she needs to spread her wings more, without that ruining her friendship. Depending on your playthrough, she may have already fucked Kate, and likely gotten frisky with at least one other person, so it holds more weight.
