She gasped when he inserted a finger inside her and tightened her grasp on his thigh, digging her fingernails in just a little. Bellatrix closed her eyes and leaned her head back against the wall as she let him explore her with his finger. Why did other girls say it was so painful the first time? It was really nice so far. Though, she had no idea how to describe the sensation. It was rather tingly, warm, and gave her a sense of falling - at least in the way one's stomach may feel as though it is dropping just before a fall.
Bellatrix initiated another deep kiss with him, getting more into it now. This wasn't bad. They just had to be careful not to make noise that would attract attention to the area. Other than getting caught, she didn't have any worries.
She moved her hand over his erection, which felt quite substantial. Much more than a finger -- so, yeah, that might actually hurt. Bellatrix tried to shrug it off; it was too late to tell him no. She truly felt a need to please him, and she did not want to say no to him anyway. She undid his pants and stroked him, hoping this was the right thing to do.