People change no matter how hard they try not to. As you grow older, you mature and with each new level of maturity comes different ideas, different needs, and wants. The person who is perfect for you at 20 could be the person you hate when you're 35. Find someone who will grow with you, change with you, laugh with you and cry with you. A person who fills in where you lack, a person whom you can fill when they are lacking.
What about the perfect person? He/she does not exist. There are no perfect people only people who are perfectly meant for each other.