It doesn't matter if your boyfriend knows how to speak French, or if he just likes the sound of the language. Either way, it can't hurt to learn how to say a few saucy French phrases.
You don't have to sign up for a class in order to learn the language. In fact, a class probably wouldn't teach you the sexy stuff that you actually wanted to know. For that information, you should check out this page from Imgur:
What other French phrases do you know that would fit right in with the ones listed inside of this book?