First as someone that desires to enter nursing school
and become a licensed nurse, hanging out with a someone uses cocaine is a very BAAAADDD idea. If the drug gets found in your residence, on your boyfriend when he is with you, or at his place when you have been with him.....you will get popped and there goes your chances of being licensed.
Background checks are done routinely and you would be amazed at what shows up. I received a thorough one for a govenment related assignment - the stuff they dug up on people that I associated with, even 20 or more years ago, was astounding. No to mention that data on my brother in law. And while some places will blow off MJ data or things that happened 20 years ago., currently dating someone that uses cocaine is not something blown off.
This also reinforces the fact that you should be using condoms with sexual activities, even where pregnancy is not a possibility. Someone that uses cocaine does not necessarily have the best judgement...if they did, they wouldn't be using cocaine, which has immense health hazards attached to it.
But a possibility that you may not have thought of. Did you explain to the screener that you had teeth removed in the last week, and that they probably gave you an injectable local anesthetic. Most commonly, drugs like novacaine....which may be in a similar drug class as cocaine.
Some solutions containing small amounts of cocaine (usually marketed under a different name) are occasionally used in oral (dental) and nasal surgery or for certain special situations of suturing, for it's anesthetic and vasconstriction properties. And there are several local anesthetics used that are of a similar class. Even if you had conscious sedation, the area of the procedure is generally numbed with something. You might ask your dentist for that data and see if there was a cross sensitivity perhaps in the drug screen.