[hannah]

You will be with the people that your soul needs to be with. If they are to be a part of your continuing soul journey, they will be by your side. If not, then when your soul is free from the emotions and desires that your material body possesses, you will be able to accept their absence with peace and love.
Your fiance not believing in the afterlife, I think that is not important. What beliefs and opinions you hold during life doesn't matter as much as what you have in your heart- love, peace, hope and happiness, that will carry your soul onwards. Not believing in the afterlife at this present time does not mean your soul will not reach it.
Lost souls are in my understanding linked to extreme negative emotions which confuse everything so that the Path is obscured.
Try not to worry about it- everything will work out the way it's meant to be.