Grief and sadness are perfectly acceptable to feel as long as you do not let them overwhelm. I had an incident occur this morning that brought me a tremendous wave of grief; it is normal to grieve loss, but it is not required that it be ruminated on. Loss is not just with people, either; it includes missing friendships, relationships, a lifestyle, substances, and so on. It is not simply limited to death. Sadness is a normal human emotion (not unlike any other) and can be readily accepted.
This is not to say it should be relished upon or one should stay “stuck”; people are allowed to feel without doing so. We may feel a sense of guilt if we do not take the matter to heart. Be careful of failing to feel or suppressing; conversely, not to live in grief and misery. Balance.