Ways to get your girlfriend back when she has a boyfriend is going to be a challenge. New relationships can be very attractive particularly to those that have had their heart broken. A new man is likely to flatter and praise their woman as well as spoiling her. They have yet to get used to having her around or take her for granted.
So what tricks can you use to get your girlfriend back even if she appears to have moved on? Well, you two have history which has yet to happen with her new beau. History means that you will have shared some incredible times that only you two know about. So why not start reminding her of that?
Your other plus point is you know this woman. You know how she thinks, what she likes and doesn't like. If she preferred you to dress a certain way, then make sure that is how you are attired every time she sees you. Act happy even if your heart is in pieces. Nobody likes nervousness, especially in a man, and pleading with her to come back to you; as your "life is not worth living without her" only works in bad movies.
Instead be happy and positive and make out your life is brilliant. She is more likely to remember the fun times you both had and may even start to miss them. Let her know that you would love to give your relationship another go but that you realize she has moved on. She will be left bewildered and question if perhaps now you might move on too. Women like to be sought after so the fact you are pretending to accept her new relationship will probably confuse her.
You could try dating other women. There is nothing like jealousy to motivate a woman into taking action. We all want what we cannot have and if you make yourself too available, she is less likely to be interested and you are less likely to get your girlfriend back.
Find reasons to unintentionally cross her path so that you can remind her what she is missing out on. But don't go pestering her as that is just going to get you into trouble with her perhaps her new man and in the worst case scenario, possibly with the law.
Your ex will listen to her family and friends, so remember to include these people in your wooing process. Remind them why they like you and would prefer her to be with you rather than her new man. If you were with your ex for a long time, you should have good relationships with her friends. Now is the time to take advantage of those contacts. If you treated your ex badly then make sure her friends and family know you genuinely regret it and have apologised for your actions. You do not want all her family telling her to stay away from you, as that will make it even harder to get her back.
To get your girlfriend back even though she has a boyfriend may be more difficult but nothing is impossible; if you want it badly enough!