My boyfriend lied to me?!?

ok so last weekend i was driving my boyfriend nd one of his m8s somewhere, my boyfriend asked me to take his m8 somewhere so that he could pick up his contact lenses, i actually didnt think anything of it, thing is, tonight he left his phone in my car, and i was curious and i had a look at his texts, which i know was totally wrong, and i feel really bad about it, but i found out that "contact lenses" was actually a pretense for something else, probably weed, i cant believe my boyfriend would lie to me! what do i do? im not sure if i should confront him or just leave it? please any advice would help...