Don: Grief can prevent you from being present in your current relationship and prevent you from starting a new one.
The pain of grief keeps a portion of your attention and awareness preoccupied until the loss is faced. Though you can push grief down to the side, in reality, ignore it, but there is no getting around it. You will, at some point, experience it. Until then, it is a part of you, keeping you unavailable to those around you. This is often expressed by saying, "They are here, but they aren't."
When you experience significant loss (change) of any kind, especially family members to death or divorce, the grief process begins and occupies quite a bit of your attention.
Until the emotional and physical realities that the loss has caused are acknowledged, felt (experienced), and accepted, and to some degree, emotional acceptance has happened, you are not fully emotionally present. Your mind is fighting the reality of the loss.
The positive outcome of going through the action steps of grief recovery is that you begin to experience more of the present moment and can better tend to what is happening in your life now. Imaginary conversations in one's head, as if the loss has not happened, are gone or only appear now and then when triggered by something that reminds you of the loss.
So, the experiences of grief happen without your control, consuming most of your attention.
If you are already in a relationship and you have a significant loss, you will be less emotionally available to your partner until the grief is processed. If you are not in a relationship, grief could keep you from making efforts to begin one until grief lessened.
This is true both with death and the broken heart of a divorce. However, some people start a new relationship to avoid and cover up the pain of the grief experience. If grief is not faced well, the relationship you begin will start on a very unsteady footing because you are not fully emotionally there and not able to be emotionally close. The new relationship will be based more on the thrill of hormones and the relief of avoiding grief. Eventually, grief will be faced in this new relationship.
The same is valid for pets. Many people quickly replace their pets to avoid the loss experience, but only later do they regret bringing a new pet in so quickly. These actions cover up, delay, and make grief more of a problem instead of a process to go through. However, with the actions of grief, recovery can happen even when it has been massively avoided. There is hope.