You want to break up with your boyfriend now, but you are afraid of things that you can't control after breaking up. That's why you dream about so many water-related things, crocodiles, snakes and other terrible things in your dreams.
On the other hand, because you hit or tried to hit these terrible things in your dream, it shows that you are still considering how to break up and make some preparations for what may happen after breaking up.
Personally, if two people really can't go on, then break up as soon as possible; But it is not easy for two people to be together. Be sure to think clearly before breaking up, whether it is really necessary.