Many cultures, including American culture, associate loss and a need to grieve only with physical death. Even then, we are often expected to quickly "get back to normal", leading people to repress much of what they feel. Coming to terms with loss is a process with many twists and turns. Grief is always complex and unique to each person and in death grief is further complicated by the nature of your relationship. If you have unresolved conflict with the deceased it is important to understand that when someone dies the relationship does not die along with them. It remains alive inside of you.
Loss actually underlies most issues that bring people to therapy. Symptoms of anxiety or depression connected to childhood neglect or abuse, marital infidelity, divorce, friendship conflict, medical illness, miscarriage, abortion, unemployment, career decisions, and even happy events like marriage or the birth of a child, all include some kind of loss. Whenever we choose one thing over another, we give up what we could not choose. Literally everything we do is a trade off of some kind. This is why some say that life is a constant stream of letting go. When loss is examined in therapy, insight and guidance allow you to fully integrate the experience into your life, and to handle it with grace in a manner that reduces your suffering. Feeling strong now, you can move forward, capable of handling the inevitability of future loss.