Answer:
It is the feeling of not being whole again because we lost someone or something with whom we shared a great aspect of our lives together.
Step-by-step explanation:
Idiomatic expressions are groups of words whose meanings may not be tied to the literal words used. There are few exceptions to this. The idiomatic expression, "lose a part of yourself", is used when people have lost someone or something dear to them. Since they might have shared an emotional bond with the person or thing, losing it seems like they have lost a part of themselves.
This part of themselves is not to be taken literally but symbolically. The person affected might feel drained and low in spirit as a result of the loss.