He told us _____ sad and that it would be better for everyone.

- In English, when forming negative sentences or phrases, the word "not" is often used to indicate negation.

- When using "not" with the verb "to be," it typically precedes the base form of the verb, which is "be" in this case.

- Therefore, the correct construction is "not to be."

Example:

"He told us not to be sad and that it would be better for everyone."

Here, "not to be" is used to indicate that the speaker is advising against being sad, and it follows the rule of using "not" with the base form of the verb.