Breakups are hard. Moving on is harder. And sometimes it just takes a little time before a girl is ready to open herself up to a new relationship of any kind - emotional, sexual, or otherwise. It's fairly easily to sense if a girl isn't totally available for you at the moment. She'll mention or relate things to her ex or become moody at certain topics out of nowhere (that, no doubt, remind her of her ex). You might get the feeling there's something more important (or someone more important to her at the moment) on her mind. Even worse, if she's still in a relationship but expresses feelings towards you, steer clear. Someone who cheats on someone else to start a relationship with you is likely to repeat that pattern in the future.