Be respectful. Explain your side of the situation and why you think the relationship can't work. Assure her than she doesn't want a relationship with someone who doesn't love her. Encourage her to find a partner that will meet her needs better than you can. Try not to hurt her feelings but don't lead her on either.

Keep your distance from your ex girlfriend whenever possible. Being near her will only reinforce her feelings that she could possibly get you back. On the other hand, if she is vindictive you need to avoid retaliation.

Be firm. If she continues to pester you, don't give her any reason to think that she has another chance with you. State your position, and end conversations immediately. As long as you continue to talk to her or see her, she will do whatever she can to continue getting the attention from you.

Keep details of your personal life secret from your ex girlfriend if you start a new relationship. She may begin to obsess about her, try to contact her and start trouble.

Take extra steps if she just won't leave you alone. Quit answering her phone calls or block her phone number if you have too. In extreme cases, you might have to file a restraining order.