Being with your boyfriend or girlfriend can be the best time of your lives. Loving and caring for one another makes you think that you would or could do anything for them. Though when another guy or girl come into their lives, that can change everything. Cheating on a boyfriend or girlfriend makes it so hard for the other one to forgive. It's hard to forgive someone for cheating on you, because even though he/she says he's sorry, it is still hard to tell the difference if it is true or not.
Also, because you thought that he/she loved you and wouldn't do such a thing yet they did and how can you forgive someone for that. Yet on the other hand, it's harder to forgive yourself. You are the one that has to live with the mistake you made, it will change your life and how some people look at you.
Some people will not want to trust you and be attached to you, because they aren't going to want to get hurt. Therefore it's a decision that you yourself made and you are the one who has to pay the consequences. Offering forgiveness is the best way to go you would always want to be forgiven. The Bible shows great messages to forgiving others. I.e. "The Parable of the Prodigal Son" Is great because the son did all his wrongs and was forgiven in the end by his father. Live your lives to its fullest, with as few faults as possible, forgive and love because you know that's what you would want.