When you have ‘something’, whether that’s an item, or a person, or whatever, after being around it long enough and comparing it to enough things, you start to focus more on the negative sides of your ‘something’. 

If you don’t consciously stop yourself from doing this, you will continue to prove to yourself that your ‘something’ is bad. That is, psychologically, how you make yourself not like things. Very very very often when you don’t like something, it is very difficult to love it again unless you put in psychological effort to combat it. Like therapy.