Be worried, afraid that
This expression indicates that the speaker did, or is doing, the action in the following clause out of worry or fear that the situation or action in the preceding clause has occurred or will occur.
The 보다 of -(으)ㄹ까 봐 means to guess or think something.
This expression can also be used in the form -(으)ㄹ까 봐서.
Because -(으)ㄹ까 봐 refers to the speaker's worry about what is stated in the preceding clause, the following clause must state the action that is, or will be taken by the speaker. A clause in the future tense about a plan of action yet to be taken cannot be used.
Indicates the speaker did, or is doing, something in the second clause because they are worried or afraid that what is mentioned in the first clause has happened or will happen.
(으)ㄹ까 봐서 can be used without changing the meaning.