Love, romance, and sex have always had a place in action/adventure, fantasy, and science fiction, but, today, the woman usually fights beside the man.
Used with care and thought, love, romance, and sex can add dimension to the characterization, plot, and pace.
Unfortunately, care often isn’t used, and the pace and plot are ruined because of it.
Recently, I read a novel about a romantic couple fighting demons. Most of the time, they were so busy fantasizing about the other’s crotch that I wondered at the brains and survival skills of these people. A fighter who is busy thinking about sex before and during a fight is a dead fighter.
The pace was also ruined because the constant sexual elements and sexual introspection distracted from the plot and the peril.
Brief bits of body language--a touch, a smile, or caress, as well as brief snippets of romantic dialogue can keep the sexual tension and caring evident without bringing the story to a dead halt.
In a lull in the fighting at a safe moment, put your couple in camp with a good friend walking patrol away from them, and let them at each other. Or find them a safe hiding place where they can repair their wounds and chase each other around the sleeping bag if they want to.
The intensity of their struggle and its constant interference with their sexual needs makes the love scene that much stronger when it happens.