This depends on what your feelings really are for her, and if you want to give up.
you wanted him because you couldn't have him, now that you can have him you no longer want him.
That means that he never really lost feelings about you when you broke up. You are his key to the lock in his heart.
Take him back
tell girlfriend the truth
because this preson still has feelings for his ex-girlfriend
Could be because she still has some feelings.
The truth is, he still has feelings for you. This other person is just to make you jelous.
It could mean several things. They may have agreed to still be friends. He may still have feelings for her. He may have other reasons.
The X, and here's why, it would be akward betwee you and your best friend if you and his sis' broke up
Do you mean How do you get your ex girlfriend to go back out with you because if she's your girlfriend then you guys are still goig out. if that was your question it depends on who broke up with who because if she breoke up with you then she dont want you anymore if you broke up with her there's a chance she might want you back just ask her.
still has feelings for her
Well this is espesially common if the girl broke up with the guy. So then it's possible that the guy still has left over feelings or hasn't completely gotten over his "ex-girlfriend".