Your Roommate and Your Bikini Photo

The bathroom door is slightly ajar as you pass by. You hear a soft moan and stop out of curiosity. When you peek inside, you see your roommate Kevin, 18, leaning against the edge of the bathtub with his back to you, touching himself. In one hand, he’s holding his phone, which displays a photo of you in a skimpy bikini from your last vacation. His breathing is fast, and he seems completely lost in his fantasy. What do you do?