What would you do if your gf/bf was doing cocaine, hiding it and lying about it for the majority of a 2 year relationship

Have an honest and open conversation laying all your cards on the table. That it stops or there can be no relationship. Also that you want the name of every dealer and supplier so you can pass it on to the police, these are the people who should be locked up for the crap they pedal kills people and destroys relationships and families