"Sometimes it's not the people who change": This suggests that individuals' core personalities or true selves may remain consistent over time. People often have certain values, beliefs, and characteristics that define them, and these aspects of their identity may not undergo significant change.
"It's the mask that falls off": This part refers to the idea that in some cases, individuals may present a false persona or wear a metaphorical mask in their interactions and relationships. Over time, as the relationship deepens or external circumstances change, this facade may no longer be sustainable, and the true nature of the person becomes apparent.
In essence, this statement highlights the concept of authenticity in relationships. It suggests that it's essential to be genuine and true to oneself and to seek partners who share similar values and beliefs. It also implies that over time, the true character of a person tends to reveal itself, and it's important for individuals to be aware of these changes and act accordingly in their relationships.