Here are some quotes about broken friendship that I found:

- "A friendship that can cease has never been real." – St. Jerome
- "Fake friends believe in rumours. Real friends believe in you."
- "Things change. And friends leave. Life doesn’t stop for anybody." ― Stephen Chbosky
- "Friendship plants itself as a small unobtrusive seed; over time, it grows thick roots that wrap around your heart. When a love affair ends, the tree is torn out quickly, the operation painful but clean. Friendship withers quietly, there is always hope of revival. Only after time has passed do you recognise that it is dead, and you are left, for years afterwards, pulling dry brown fibres from your chest." – Anna Lyndsey
- "When trust is broken, so are friendships."

I hope these quotes help you.