I don't think that's entirely true for Leliana, there was obviously the more adventurous parts of the bard lifestyle yeah but even then she was shown to be very set on and possessive of Marjolaine.
And the warden, for that matter.
Morrigan and leliana were written as foils to one another, but as with most bioware examples, It's not simple and one dimensional. Leliana is--or rather, was--the more worldly of the two but she's embraced an utterly compassionate and selfless worldview as a way of life. Morrigan had that nasty Darwinist streak but it's implied to be a direct result of Flemeth's influence. Morrigan is, in many ways, the more innocent of the two, yet she requires a much lower approval rating before she'll sleep with the Warden than Leliana does.
Similar comparisons can be made between Isabela/Merrill and Ashley/Liara. The "nice" one is not always the more innocent and so on.
Looking for a clean cut Betty/Veronica dynamic in a Bioware game is an exercise in futility. Edit: I point this out because it sounds a little like that's what you're looking for, Ishten, and I just don't think you going to find a "more virginal" example between Josie and Cass.