Watching my wife kissing her lover in the throes of passion gets me stiffer than a rock. On our very first experience, I asked her not to kiss because that was too personal and I wanted her to fuck just for the thrill of a "strange" fuck and that's all.
After her lover had her panting and ready to receive his cock, and seeing the passion on her face, sure enough, ....... she let him kiss her, as she looked my way with a look that said "sorry, ... but."
Now I'm hooked. She is by FAR more "giving" when she is kissing her lover of the night.