The range of opinions is interesting...
Carmel raised a good point about TV/films. To me it's kind of inconsistant to allow kids that age to watch films that portray exactly the same thing (intimate non-married relationships) and then veto it happening under the roof. If you control what they watch to the same extent as your houserules, then, fine, no inconsistancy.
To me a parent remaining credible is important. I saw my dad stop drinking before meetings (as in wine with a meal) after some half-assed Watchtower about how the Priests of the Temple wouldn't stand before Jehovah intoxicated... and saw it forgotten about within a few months... I saw my parents react negatively to song lyrics no worse then the Song of Soloman and take refuge in 'Because I said so' when the inconsitantcy was pointed out.
Your kids know you're going through a period of change. I don't know about your 12 year-old, but if your 14 year-old is anything like my 13 year-old, then you'll be able to ask her how she would feel in situation a and situation b, and how you're deciding which would be best, and how this is confusing because of what you used to believe.
Even if you don't change your mind as a result of the conversation it's a fantastic opportunity to foster maturity in your daughter.