bubble = feeling great and important or successful or any great feeling Example: You pass all your exams and you feel great. That is your bubble. Someone comes and tells you your computer has been stolen. That bursts your bubble. OK?

To burst someone's bubble means to destroy an illusion or delusion or someone's fantasy or to tell someone unexpected bad news. 'I don't want the bubble to burst' = I don't want to be disillusioned.

it means I don't want to break your words or make you disappointed

There are two possible meanings: 1. "I don't want to burst your bubble, but ..." (= I don't want to disappoint you, but... [some disappointing news]) 2. "I don't want the bubble to burst." This could refer to an economic "bubble," for example the price of houses in the United States (the "housing bubble"). The price went up and up and up, but then suddenly the bubble burst -- after that prices went down quickly. So "I don't want the bubble to burst" can mean "I don't want the prices to fall."