Describe their physical environment in detail. If it's a cold night and they are huddled together for warmth before their first time, it can create an atmosphere of closeness and vulnerability. The small details like the softness of the bed or the flickering of the candlelight can enhance the emotional impact.
You can focus on their internal thoughts. For example, Jess might be thinking about how Nick has changed her view of love and how she's finally opening up completely to someone. Nick could be thinking about how Jess makes him want to be a better person. By delving into these deep thoughts, it adds an emotional layer.
Use flashbacks. Maybe show moments from their past that led them to this point. Flashbacks of their first meeting, their first argument, and their first kiss can all contribute to the build - up of emotions. It shows the journey they've been on and makes their first time more meaningful and emotional. Also, don't forget to describe their facial expressions and body language during the moment, like the way Nick looks into Jess' eyes with so much love and Jess blushes slightly, which can convey a lot of unspoken emotions.