When you are dating someone, his ex has no place in the picture. If your boyfriend's old girlfriend keeps coming around, you have a right to speak up and, if you can, put a stop to it. Avoid any heated confrontations with her, but take charge and let it be known that you don't put up with an ex in the picture. You don't have to ever lose your cool.
Make sure you and your boyfriend are on the same page. Tell him you want to understand his feelings about the situation, and you want him to know how you feel. Open up communication about the ex-girlfriend, and you can actually strengthen your relationship with your boyfriend. By communicating instead of confronting, you can find comfort in knowing how your boyfriend feels about you and showing him that you want to hear his feelings on the subject of his ex. At the same time, you will have the opportunity to let him know the situation is bothering you.
Examine yourself. You may have jealousy issues because of a history of being cheated on. That doesn't mean your feelings about the presence of the ex-girlfriend are not legitimate, but it may help you to cool down a bit and realize you bring some issues to the table. Taking a position with your boyfriend that you take responsibility for your own feelings can go a long way for helping him feel like you are not attacking him.
Ask him to change his cell phone number. Your boyfriend can let all his friends know his new number, and he can advise them not to give it to the ex. She can't call or text if she doesn't know his number. If he refuses, it might be an indication that the previous relationship isn't finished.
Ask your boyfriend to block her email address from his address book. Most email programs have a blocking feature. This will prevent her from getting hold of him online. If he can't block her, persuade him to get a new email address.
Ask him to eliminate her as a friend on social networking sites. Your boyfriend can block her as a friend or any other kind of contact on his social networking pages, and she won't be able to snoop on him and write to him there.