Gravitational forces add together.
For instance, if you were to pass between the Earth and the moon at the right distance, the moon will pull you one direction, the Earth will pull you the other, and gravity will cancel out. There is a concept called the gravitatinal potential, which is a measure of the strength of gravity. If one star starts to expand, it may reach a size where the gravity from its companion star pulls on the gas stronger than the parent star's gravity, and the gas will then fall onto the companion star. As for the planetary alignment in May, the force of gravity falls off like the square of the distance from a planet. So, if you double the distance from a planet, the force of gravity is four times weaker.