I have a boyfriend but...

So I have a boyfriend we've been together for 11 years and have a son together. I know 11 years and not married, we were engaged, then separated and officially got back together 3 years ago but lately I have been wanting a special female friend. I have been with women before and he knows that. Although I find women attractive and sexy, I don't want to date them I want more of a fwb situationship; but I don't know how he will take it. Should I have my fun and be like oh we're just friends or tell him the real deal?