Of course they do.

John motioned for Cameron to put her gun away, then did the same before walking casually into the room.

“Hey Riley, how you doing?’

Riley froze with one hand buried in her snatch, while the other one had just began to pinch a rosy nipple. “Ah, hi John,” she said, her face turning a deep shade of red. Riley wanted desperately to cover herself, but seemed unable to move. She couldn’t even get herself to remove the hand that was still shoved halfway into her pussy. “Maybe you could go for a minute, as you can see I’m kind of... busy.”

“Oh, I don’t mind,” John said as he sat down next to her and started to grope one of her breasts. “And nether does Cameron,” He replaced his hand with his lips, sucking as much of her tit into his mouth as he could. Riley mound despite herself. She really should stop this. On the other hand, he was her boyfriend and what he was doing felt really good.

But she should get rid of Cameron, right. Riley looked at the other girl. She stood there with her head tilted to one side, her eyes torn between her ‘brother’ suckling Riley’s breast and the hand that Riley still had inside her groin. She found the sight strangle erotic.

You see, Riley was bisexual. While she found guys hot and was very attracted to them, she tended to think the same thing about girls. And at that moment all she wanted was to rip the other girl's clothes off and feel her naked body rubbing against her own as John fucked them both. Just the thought of it caused her hand to move inside herself again.