It's normal. Hey, you're with him happy and all, yet you have to fantasize. As you can (well, do) have him, it's natural that a part of your fantasies go to other men. As long as you do not take the step of making it real, and you don't tell him you think about that (great confidence killer for him, in himself and in yourself).

And about what you are, what you do... do not radically change, but just watch yourself. Are you starting to look like a boy in your facial expressions? Try to avoid that, well at least when it's something you can do. Do not go against who you are essentially, because that would be bad for yourself first, and probably for your couple then, but just... take care. So that he sees you've taken note of what he said to you.

That's my piece of advice, take it for what it is.