God has a reason for everyone that has disappointed us.
God allows people to let us down, because most of the time, we make people our god by depending on them. God wants us to depend on Him.
Therefore, those you lean on, were meant to disappoint you, so that you may see God as your source.
Proverbs 3:6 (KJV) – in all thy ways acknowledge him, and he shall direct thy paths.
I Peter 5:7 (KJV) – casting all your care upon him; for he careth for you.