Do people really change?

Okay so I have this friend who used to be my best friend but that was like 5years ago and we went to different schools and lost touch. Now we go to the same school but we hang with different people and for some reason we just can't get back to the best friends we were. so I was wondering. do people really change? or do they just change their personalities to fit in with certain groups? hmm I wonder?
Do people really change?
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