Changing you or allowing someone else to control you means you are not staying true to yourself in a relationship.
When I say relationship, this can not only mean a love relationship but also friends and family. You are either changing yourself to fit the relationship or allowing someone else to change you to the person they want you to be, not the real you.
This doesn’t mean the being on your best behavior on a first date or just meeting someone.
What I mean here is you either change your whole persona or allowing someone else to control what you do, say, wear and the list goes on until you are not the real you.
Think back to your days in middle school or high school. You wanted to fit in to a certain clique of people so you start dressing like them, acting different and sometimes even turning your back on childhood friends because they didn’t change to fit in to your new crowd.