FWIW one of the things drug addicts do is to cheat. My experience is that they want to live a double life. the life with you is the upstanding and responsible facade.. the Look good to the Public life.
Then there is the "other life" with the drug addicts and dealers and women who are also addicts and users. The cheating side of life (be it cheating with drugs or sex or both).
Sorry your son had to find it. Best that you know. Get tested for every STD out there AND retested every 6 months until you are sure you are clean.
Stay out of HIS bed. Your life may depend on it. You sure don't want your kids growing up being raised by a drug addict.