how a girl keeps a guy

when a guy fucks a girl in the butt and the girl squeezes her anus around his cock, then his cock feels more pleasure from increased tightness, 

then when he pulls out his cock from her butt and she sucks on his cock, 

then his cock feels vacuum instead of pressure 

the change from pressure to suction makes his cock feel more pleasure and his ejaculation in her mouth might become more intense which might make the girl more satisfied