Well in my opinion people dont change they remain the same. The thing is people tend to behave differently in different situations and we start to think that the person has changed but the fact is we never saw the other side of the person which was always there.
For example you meet a person who used to love you and then after some yrs you feel that the person doesnt treat you the way he used to.
He hasnt changed its just that the circumstances changed which is now making him/her do what they are doing.
BUt then again, its just my point of you.