He was taking special care to let the energy trickle out in drops so her body would have time to use it. She wanted more and her body was trying to suck him dry of all his vampires energy and dark magic. He didn't let her have more than the current flow rate so it would not stop but she couldn't take too much.
He groans and fucks her happily as her imprecise control of the new energy made his cock swell inside of her. Her breasts were pleasure too hard and she felt like it was taking all her will to control the power and not use it all up. As she sucked more out she felt him swelling inside and to match the thickness of her thigh. It was a slow swelling due to hjs own self control and she was feeling him holding back the effects.
That made her whine and want him to let the power do as she wished knowing sudden change can hurt if she wasn't careful. Saftly didn't matter 5o her anymore. All that mattered was his cock his power inside of her as much as she could take. Several loud heavily heated moments pass as his cock swells firmly to the thickness of her thigh and the pressure was going to make her insides rip.
He was careful to slow sown as he swelled but he didnt pull out or thrust less deeply. He continues pushing as deep as he could wanting to keep giving her more of his love.