Hmmm... I'm kinda torn on this one.
I'm leaning more to the idea that they had sex though... It just.. makes more sense if they did it. The entire book series, PP was building up this massive anticipation of the Adam and Eve and temptation thing. It just doesn't make sense how their kissing and true love is what can change the universe. I don't see how only their love and kissing is SO special over everyone elses... and falling in love and kissing isn't considered sinful. Sex isn't sinful either but to have premarital sex, in the christian world, is sinful. The witch's prophecy said that Lyra (Eve) would be tempted by the tempter (Dr.Malone/Serpent). SOOO, it needs to somehow parallel the story of Adam of Eve to make some sense. After the serpent tempted Eve and she and Adam ate the forbidden fruit, their eyes were suddenly open and they covered themselves with leaves. Remember when Lyra was saying that she used to swim naked all the time with Roger and her other friends without even thinking about it, but with Will it was totally different? She couldn't just strip naked and swim in the water with him without feeling... different. This is very similar to how Adam and Eve were very comfortable walking around naked with each other but once they ate the fruit, they covered themselves. Lyra was comfortable naked with Roger, not all that out there with someone she has feelings for.
Dr. Malone tempted Lyra by telling her the story of how she fell in love for the first time when the boy put the marzipan to her lips. As Lyra and Will are eating while taking a break from catching their Dæmon, Lyra takes a piece of FRUIT and places it to Will's lips. Eve gave fruit to Adam. Then they suddenly both become aware of each other's feelings for one another. Eve and Adam's eyes are open. They lose their child innocence by experiencing a feeling they've never felt before and soon after, once they go so far as to touch each other's Dæmon, the Dæmon change into their permanent form, just as Adam and Eve's stopped changing forms as well (in the Golden Compass Dæmon version of Adam and Eve).
In the story of Adam and Eve... Adam and Eve have sex... so that makes me to kinda believe that Lyra and Will did as well since the stories are so paralleled. (And... after the horrible experiences they've gone through, I wouldn't blame them for going crazy with each other. Plus, they are pretty daring characters..)HOWEVER, I found this while I was writing this post and it really confused me. Please let me know what you make of it.
The Amber Spyglass: Preemptive Absolution. US edition.
"The child, then, is in the position of Eve, the wife of Adam, the mother of us all, and the cause of all sin."
"Please, remember- the alethiometer does not forecast; it says 'IF certain things come about, THEN the consequences will be...,' and so on. And it says that if it comes about that the child is tempted, as Eve was, then she is likely to fall. On the outcome will depend... everything. And if this temptation does take place, and if the child gives in, then Dust and sin will triumph."
What if the sin were to be if Lyra and Will gave into their love and decided to leave an open window anywhere, causing the world to eventually end? Because it's saying that she needed to make a choice and the choice is what would make or break the universe. They DIDN'T become Adam and Eve. She was LIKELY to fall. Not for sure to fall. Sure, they followed the story of Adam and Eve... up until they needed to make the crucial decision. They could have been the next Adam and Eve by leaving another window open, getting married, and having a family, thus eventually ending the life by having Dust leave completely. But.. then that confuses me too. lol. Because it says "then Dust and sin will triumph." Well... if they both left a window open, Dust wouldn't triumph... it would leave completely. Gaaaaa I'm so confused. But tell me what you think about this.
So maybe they didn't have sex since in the end, they didn't experience the final part of the story of Adam and Eve.
UGH. I have no idea lol. WHATEVER. I'm still sticking to my initial thought of them making love under the trees or wherever the hell they were.