With anger

The intense heat in the room had shortened tempers, including mine. I exploded. "Disgusting? I'm fucking 18 years old! Sometimes I check you out! Both of you! Hell, I've jerked off over you more times than I can count! You wanna know about RESPECT?! I've had the hots for both of you for as long as I've known you, and this has been made a helluva lot harder since you both suddenly became my sisters, but you know why I've kept this to myself? Out of fucking respect!

"Maybe you should get off your high horse and take it as a compliment that I think you've got a hot ass! And maybe, just maybe, you could show ME some respect and cover yourselves up a bit, for my sake. Especially you, Jessica!"

I stopped, panting. I was being completely unreasonable and spiteful. I knew I was. But I couldn't stop the rage from pouring out of me. All those months of pent up frustration, the shame of being caught, and the overbearing heat had all run together inside me.

Marisa started at me, stunned. Then her eyes started to well up and she suddenly darted out of the room. There was a slam as the front door closed.

"Nice one, asshole," said Jessica, as she turned to go after her sister.

I slumped into a nearby chair, immediately regretting everything I'd said. It looked like I had a lot of work ahead of me to undo this mess.