It's a good thing she's usually not satisfied after just once, because at the rate he's stretching her she's not going to be done with one. But he's getting close to how wide she can stretch to accommodate him... he'll start having quite a bit more difficulty from here on, though she would hardly complain if he tried stretching her further. He probably won't hit a limit depth-wise, with girth she's trained for depth... to an extent. But he would have to get at least another six inches in to hit her usual limit.

Her hands come up to rub at the bulge he's made in her belly, impressed and amazed at him. Feeling him squirming inside of her like that... well, that's all it really takes to push her over for the first time. Her muscles tense and she lets out a long, trailing moan as her cock starts pulsing inside of him and filling him.