A boyfriend will only forgive once he is ready; it is impossible to make someone give forgiveness. Boyfriends will only give their forgiveness once they see that the girlfriend is truly sorry for what she did.
If the girlfriend made an honest mistake, he will likely be more quick to give her his forgiveness. Things like cheating, lying and even stealing are harder for boyfriends to get over because they break trust. A good girlfriend will admit to these mistakes and let her boyfriend know that she did these things. A girlfriend should also make sure that she has the patience to wait for her boyfriend to forgive her.