He knew he was staring lustfully as she entered the bedroom, but he couldn't help it. Lucy had always been lovely, but seeing her in all her glory made Tumnus realize that she was perhaps the most gorgeous creature in all of Narnia. A buzz in his groin told him that an erection wasn't long in coming, and it required all his strength not to overtake her immediately.
Instead, he walked over to her and gently kissed her lips. As he rubbed her bare back he began kissing her neck, then her full, melon-shaped breasts. He was barely aware of her nipples hardening, and that was his cue to place a hand on her hip in order to guide her to the bed.
Tumnus lay on his back with Lucy perched on his hips. She began by massaging his chest and belly, but it didn't take her long to find his "sweet spot". As Lucy used her fingertips to lightly tickle his belly button, Tumnus felt his penis stiffen. He was as gentle as possible as he entered her, and he placed his hands on her hips to help Lucy keep her balance as she moved her body in sync with his. The expression on Lucy's face was originally one of pain, but it lasted only a few moments before changed to one of bliss.
Slowly, gently, Tumnus exited her body and guided Lucy to switch places with him. Balancing himself carefully over her stomach, with one furry leg on either side, Tumnus began to rub the tip of his penis over her belly and chest. As he guided it around and between Lucy's breasts, he was almost certain that she involuntarily gasped with pleasure.
It wasn't long before he felt Lucy using one hand to playfully squeeze and massage his scrotum, while using the other hand to gently twist and tug on his penis. He soared into seventh heaven when he realized that she had placed his penis inside her mouth; she was alternating between rubbing the tip of her tongue over his penis' tip and gently biting it.
Tumnus was fully aware that Lucy saw him as nothing more than a friend, and he was okay with that. He cared for her much the same way; the difference was that even though he considered her his closest friend, she was also his queen. Anything she desired was hers if he was able to grant her request, which was why he'd agreed - albeit, somewhat hesitantly - to have sex with her.
Lucy had told him that she needed some time where she wasn't required to behave as a queen, and while he knew that she'd desperately wanted a night free of her royal duties, Tumnus also realized that it wasn't possible for her to spend the night with him, or her family would come looking for her.
Lucy was still nibbling on his penis, while continuing to playfully pinch his scrotum with one hand. With the other, she'd begun to fondly caress the inside of one of his thighs. Tumnus told her that he felt it best for her to bathe and return to Cair Paravel. She removed her hands from his scrotum and thigh and she let go of his penis. Tumnus moved from on top of Lucy so that she could go to the washroom.
He remained on the bed and allowed his eyes to take in her bare back. He watched her hips and her buttocks swivel from side to side, carrying her delicious, seductive body away from him. His groin buzzed again, hungry for more of what it had been offered. But Tumnus had not asked for tonight, and he didn't feel comfortable asking for a repeat of what had not been his idea.