Tell him who you are

You quickly lock the door and check everything to make sure you two aren't interrupted. Then you look at Brian who's still looking forward to "celebrating" with Diana. "Oh, look at you" you begin saying "still hoping you're going to get laid tonight." You can't help but laugh. "Sorry Brian but that's not going to happen... well at least not the way you hope it would." He looks at you confused. "What the hell are you talking about Diana?!" He asks you. "Well, what I'm talking about is that you're not really talking to Diana right now!" You say, giving him a hint already. "So, what you're saying is ..." "IT'S ME, John, you dumbass" you interrupt him, laughing in Diana's hot body. "Wait, what ... nonono ... never!" He says, still not believing you. "Okay" you begin "but would Diana know that you jerk off to her and her sister regularly?" He looks at you in shock. "Would she know that you've secretly made a photo of Diana and Chelsea while they were in their bikinis when we all were swimming in their pool last month, and that you even sent it to me?" The thought of that photo of Diana (meaning YOU right now) and your older sister Chelsea made you wet again. It was a perfect photo, taken in 4k. Both sisters were just about to get into the pool as Brian took it. You could perfectly see Diana's and Chelsea's tits, with their bikini tops showing very much skin. Their big asses could be seen perfectly too, and again they weren't much hidden by their bikinis either. You both have jerked off to this picture many many times and you see in his eyes that he finally believes you.