"All the brothers of a poor man hate him; how much more do his friends abandon him!"
This is the final extension of the idea in verse 4 and verse 6. Deep friendship is begun and built on the idea of mutual benefit. This verse deals with the negative side of friendships. When friendships dissolve or come apart, it is because the benefit is not high enough for the gain.
Notice the idea that a person who is poor or who has nothing to share is abandoned. Now this is not talking strictly or even mainly about money. It is talking about the nature of friendships. What is the benefit that you have? Are you developing it and being generous with it?
In what areas are you rich? Where can you increase your wealth? Is it your personality, your looks, your intellect, your attitude, your wisdom, your connections, your parents, your abilities, your work ethic, your follow-through, your diligence, your money, your other friendships, your listening skills, your people skills, etc.?
Just because a person does not have an extra amount of money does not mean that they are poor. Being poor is having nothing of value to share with potential friends.
It is often hard to get teenagers to realize their own wealth because other kids may see them initially as being poor or having nothing to bring to the party. Every person is wealthy if they will develop what God has given them.