Love scenes in novels aren't made believable within the confines of that single scene. Usually. Certainly writers can do plenty within the scene to kill the mood or break a reader's willing suspension of disbelief. In my opinion (and subsequently, in my craft practice) love scenes are made believable by virtue of the journey that led up to the sex scene. If a story goes straight for the sexy times right from the outset, then the journey has to be implied within the context of the scene.
It's no secret I like smart heroines. It may, therefore, be no surprise that in order for me to believe my heroines would hop in the sack with someone, I need to believe that decision would make sense from within that heroine's point of view. This is why I need a journey to a love scene. That journey is a series of small vignettes that put pins on a map taking my characters from strangers, even opponents, to trust. No. Not to lovers. To trust. Lovers comes after trust has been established in my books. No trust, no nooky. Of course there are heroines who would hop in bed with someone they don't trust. If that's going to happen, however, I, as a reader, need to understand her motivation for it. Is this a trauma response? People pleasing at enormous cost to herself? A rebellious move? A revenge screw? I can buy a lot but I need to comprehend why someone is willing to put themselves into the most vulnerable of positions with an unknown quantity. I suspect, in this post Me, Too era, when few of us are privileged enough to get to ignore just how dangerous simply existing can be for female presenting people, most of us need to get inside someone's head when they're going to engage in (perhaps fatally) risky behavior.
BUT. This isn't a murder mystery so we're not hiding corpses yet. We're still trying to get folks between the sheets.
The path from Hello to the bedroom (or wherever) is sign posted by the scenes where the first sparks of attraction fly, and in the scenes of discovery - these are the ones where characters are learning about one another and are finding the good and admirable - and in the scenes where the learning about one another starts paying off because they aren't just talking at one another anymore. They're communicating. Mostly. Coming to understanding. If I'm doing my job, somewhere in those scenes, my characters aren't just melting one another's hearts - they're melting the reader's as well. IF that happens, the love scene will likely be believable.
Barring my attempts to do something anatomically impossible, but that's another day's rant.
