Where in the Bible does it say “You should not keep secrets. Your answer should be yes or no.”

Answer:

I believe this is probably the verse you are referring to:

James 5:12 But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay; lest ye fall into condemnation.

Sincerely,
Pastor Brad