Calcifer suggests, essentially, that Sophie isn’t going to get to spend much time with Howl until he’s finished pursuing his latest love, and there’s no telling when that will be. Put another way, Sophie is going to have to find new methods of discovering what the contract is. For that matter, Michael implies that this will happen again, since he suggests that Howl is almost always pursuing women. It’s interesting that Calcifer has now twice referred to Howl as “heartless.” A single use might not have meant anything, but this is, perhaps, a clue that Sophie ought to pay attention to.