Leaving or staying at the beach house is not the important thing here. As mentioned above, the situation is temporary. Do what you need to do to get through it, whether that means leaving or staying.
The really important thing about this situation is the LESSON. As in, do not take his word anymore. Do not put yourself in a situation where your comfort/happiness/well-being depends on him doing what he said he would do. As long as that is what you take away from this, leaving or staying is really inconsequential.
L