I once heard a line in the movie "Staying Alive" where an actress says, "Everybody Uses Everybody".
I suppose when you think about it we are only with people who have qualities we admire whether that be (good looks, money, connections, personality or whatever... which we feel "enhances our lives" in some way). Not many people are out there saying they are looking for someone who "has nothing going for him or herself!"
There is always a "reason" why someone is with you rather than with someone else. Whether you interpret that as being "used" is pretty much on you. Keep in mind you always have the final say when it comes to allowing people into your life.
The only way to get "used" or taken advantage of is to put yourself in that position. At some point YOU said "YES".
You give away (your power of choice) when you start to play "the blame game" for a poor decision YOU made. Hopefully with experience comes wisdom to make better choices of people we connect with in the future.
Each of us chooses OUR own friends, lovers, and spouses. There is no escaping this fact.
In a perfect world two people will compliment one another by bringing things to the table which each of them needs.
Thus we have the term "Win-Win" situation!
Know what you want and never settle for less!
You are responsible for YOUR own happiness!