These are serious charges and you need the best defense possible. Federal drug charges carry heavy penalties. Your statements are damaging and you have been threatened. You need to contact a competent federal criminal defense lawyer and don't make any statements to any law enforcement or your co-defendants going forward.
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You should exercise your right to counsel and your right to remain silent.
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You should definitely consult with a lawyer as soon as possible. CJA lawyers and Public Defenders are good lawyers; however you cannot get a court appointed lawyer until you are arrested. A private lawyer can speak with the U. S. Attorney and possibly protect you from "David". You may even be able to avoid being arrested.
Obtain a private lawyer or request a court appointed lawyer ASAP.
Please do NOT use this answer/response to say or do anything regarding your situation. This answer/response is based on the information provided in the question asked and requires a much more complete context than is available in this public forum. BEFORE you say or do anything consult with an experienced Federal and/or state criminal defense attorney in your jurisdiction who will listen to you and your concerns.