You want your partner to reach their potential, so you are always pushing for them to better themselves, but people do not appreciate that.  People usually only change if they are forced to, so they may see your help as obtrusive and an attack on them.  They ask why you’re always harping on them when you are only trying to help them.  Eventually, you end up unhappy and they resentful because they know you are not happy with who they are.  So when they are not happy and see this imbalance, some of them will try to bring you down to their level by lowering your self-esteem.  It is a defense mechanism, and does not mean that they are a bad person.   It’s not done out of malice, but from a source of fear.  It’s important to remember that when you look back.  Most people never intend to set out to purposefully hurt you.  They only hurt you because they do not know any better.  To see it this way lessens the hurt you hold after a relationship ends.  When you are with someone who is on the same level as you, you can simply enjoy the relationship instead of constantly bickering about the person changing.  Leaving someone does not mean that they as a person are beneath you.  It only means the person they are right now does not value the same things that you do and you deserve someone who does.  They may change and you may miss out on who they may become, but you did not deserve the person they were when you were with them.  You deserved someone on your level.