If it's like that, then just handwave the sex scene or fade to black. Use one line to say it happened, then another line highlighting whether it worked or not. You don't need to detail it out. "They walked into the room" and "When they were done, X stared at the ceiling, blah blah blah." If the point of the scene is to show a lack of intimacy, then don't show the intimate parts. Focus on the numb feeling at the end, or the isolation, or what have you.