Phobia of Losing, Missing Someone Love , Close to You Name

Though it is natural to have fear of losing someone. Or anxious about missing or losing family, friends, spouse or kids. 

Thanatophobia or thantophoia is the phobia of losing, missing someone who is super important, close to you or you love. 

It is originated from Greek word thanato which mean death and no need to explain phobia which mean fear. It is also used for fear of death.