How common is it for other losses to come to mind when a new loss occurs?
This happens quite commonly. An experience of grief brings to mind those other times when someone or something left us and we felt alone. That can intensify the feelings that are already there. It’s also true that if one has not entirely resolved one’s previous losses, those memories will likely come to the fore with a real urgency. That is their way of wanting to work themselves out so that one’s full health is eventually restored.