Is it wrong not to tell him?

My boyfriend is super old fashioned and he is adamantly against marijuana. It’s legal in my state and before we started dating, I liked smoking occasionally with my friends. Today my friend and I finished a psych exam together and so we decided to grab some food and go back to the house and we decided to smoke a little bit.

I told my boyfriend all about our plans and our day, but I left out the part where we smoked. Is that wrong? Should I tell him? I didn’t do it in OUR house, and I genuinely don’t feel like I did anything wrong, I just know that he doesn’t like it and I don’t want him to get worked up.

Part of me feels like I’m a grown ass adult and I can smoke every now and then if I want to, and the other part feels guilty for NOT telling him, just out of courtesy.

What do y’all think?