If you're a young man that's been around a bit, then you probably have an ex-girlfriend. You may have broken up on good terms; you may even still care about her. You may see her from time to time or even occasionally still hang out with her. There's nothing wrong with this so as long as she knows that it's just a friendly thing. Depending on if you have somebody in your life romantically at the moment you may want to set a few guidelines as to just how friendly you can be.
The problem comes when you're single at the moment and she's single at the moment. They're going to come a time when both of you are going to feel lonely and vulnerable. This is when spending casual time together can get dangerous. Not dangerous in the sense that you're not safe, but dangerous meaning that there are still feelings involved that neither one of you have gotten over yet. Or if this is not the case, both of you just may be in the mood for a little physical intimacy, especially if it has been a long time coming for the both of you.
If you're the man, you have to make sure that your ex-girlfriend understands that you don't want to get back together. However you can confuse a woman if you sleep with her after you are broken up. Whatever the circumstances are you should try your best to avoid sleeping with the ex-girlfriend because this will send her the wrong message. If your ex-girlfriend is feeling lonely, and you're feeling lonely, there is nothing wrong with spending a little time together to cure that loneliness.
Of course this in itself can have consequences. Your ex-girlfriend may believe that you still harbor feelings for her and if you never said that you didn't then she has every reason to believe that there can still be something between the two of you. She may begin to come around more. She may begin to call you more or even inquire about spending more time at your house. If this is the case then you have definitely sent the wrong message.
If you're ex girlfriend is single and you're currently involved with somebody, make sure that you don't disrespect the person you're currently with in favor of the ex-girlfriend. Make sure that you let your ex-girlfriend know that what you and she had is over. The two of you can still remain friends, but that's all you'll remain is friends and nothing more. If you're not afraid to speak and you let her know these things then there can never be any confusion. The only confusion comes when you're confused and don't know what you want, make sure this is not the case. Make sure that any ex-girlfriend that you have in your past remains just that, in the past. Giving them any reason to believe that there can still be something when you know that there's no chance isn't the way to go.