Most Helpful Guy
Being it's not always easy to be honest, specially if you still have feelings and is hung up on that person. Sometimes you gotta do the hardest thing and simply move on, let go and let that other person be happy with someone else. If the relationship is very unstable and it has no chance of working out in the future, it's best to let it go now than be more invested and waste more time with one another1
Most Helpful Girl
God I wish I knew.
For some guys, I think it's that they know they want to be over, they know they care about the new girl, so they don't want issues/fights or to hurt the new girl, so they don't say anything in the hopes those feelings will go away.
For the guys who keep talking to the ex, it's because they're just getting a mean time girl until they can get the person they love back. They may even convince themselves they love you, but ultimately, the ex would win over you if she becomes available or he'll pine for her forever.0