Perhaps it would seem strange to any outsider witnessing the exchange that a man would press his body against his woman's when there was a dead body only a short distance away. If Hermione allowed herself to think about the murder that she just witnessed, she would've pushed him away. But, the rules that Death Eaters lived by didn't always match up with those who hadn't taken the reckless and foolish step to pledge their eternal loyalty to Lord Voldemort. Their lives were more dangerous and chaotic than the average person's, especially in those first years of the regime. Death and sex often went hand in hand. One way to celebrate that a person was still alive following the uncertainty of battle was to indulge in the most carnal and selfish of acts.