Just be mature about it, and tell him you've moved on with your life and he needs to do the same. There's no need to be snide and hurtful. You don't say who did the breaking up, but I suspect it was you. If, however, he was the one who broke up with you and you think he's now playing a game to get you back so he can repeat breaking up--you could send him a message saying "When I think of you, I think of four letter words, and L-O-V-E is not one of them". That's only to be used if he did the breakup, however. If not, don't be ugly.