Apologies are a necessary part of human relationships and are healing for both the person apologizing and the person receiving the apology. When an apology is required years after the fact, however, the process of saying you're sorry takes on added dimensions and complications. How best to proceed with a long overdue apology depends on a number of factors related to the nature of the offense and your current relationship with the person.
For Them, For You
If all goes well, an apology is a healing experience for both parties. Nevertheless, be aware of whether you plan to make this apology more for your own sake, the other person's sake, or both equally. If this apology is mostly for the sake of clearing your conscience and feeling better about the situation, take care that you don't behave in a manner that's going to cause the other person more hurt in the process. For example, he may not wish to be reminded of the incident or may not wish to have contact with you, in which case the apology will give him more pain than relief.
Choosing a Method
Decide whether to make the apology in person, over the phone, or through a letter or email. Consider factors such as how close you are to the person now and how serious the incident you're apologizing for was. Email is a good option for a relatively minor incident, but it's also a good choice if you think the person won't want to deal with you in the flesh or hear your voice. Use a written letter if you'd prefer to stay out of close contact but also want to make it clear that you take this apology seriously. With a close friend, consider finding a time when you can catch her alone to have the discussion, or tell her you want to meet to have the conversation. Plan a meeting for the purpose of apologizing only if you think it's likely you'll be having a long talk about the issue. Otherwise, making an event out of the apology could get awkward.
Demonstrate empathy for the person by expressing an understanding of the feelings your past actions elicited. Describe the situation from his perspective in both emotional terms and practical terms as needed. Give him an explanation of why you made the mistakes you did. Describe factors that caused you to overlook or misunderstand his feelings or why you were driven to do something insensitive or cruel at that point in your life.
Allow the person to forgive you on her own time. Leave the apology open-ended and do not ask for forgiveness. If appropriate, ask if there's anything more you can do to remedy the situation. If she does say that she forgives you or that she would like to work to be able to forgive, tell her that you are grateful.