I’ve lost a large number of members of my family and friends.
It is normal for you to have these fears/ doubts at this time. Remember that when this happens, it is time to simply put your trust in Jesus and remember the words of the Divine Mercy prayer: "Eternal God, in whom mercy is endless and the treasury of compassion inexhaustible, look kindly upon us and increase your mercy in us, so that in difficult moments, we might not despair or become despondent, but instead submit ourselves with great confidence to your holy will, which is love and mercy itself."
You might try praying the Divine Mercy chaplet for yourself and for the person who may pass away. It is a good prayer especially if you say the full version with the opening and closing prayer (I posted the closing prayer).
When your loved one crosses over, that is the Mother of All “Difficult Moments”. It is rubber-meets-the-road time for your faith. You will indeed see the person again, in fact even should they die they will not be all that far removed from your life. You are simply entrusting them to God for a short while while you complete your earthly tasks.
As the angel said to Mary, “Do not be afraid.”