I've never really felt used except for once with one friend. She knows I hate letting people down and especially hate telling people no. And, of course, uses it to her advantage. Oh well, the good things about her usually outweigh the bad anyway.
It can help to not confuse the intimacy of someone else sharing their problems with the intimacy that comes from someone who is willing to listen and be there for you. I don't know if there is a way to reframe the experience of listening to others as not being as intimate as you might interpret it currently. When younger I had trouble making friendship and was a "foul-weather friend" quite often, but then the people would disappear afterwards. I was lonely, but used the fleeting connections as a useful way to fill in the void. I tried to learn something from each person about how people think. I used it to analyze and gain knowledge when I didn't have the social skill to gain friendships.
I think it is easy for idealistic people to assume others will react the way you would if someone took the time to listen to you. The people who make you feel used think and experience that opening up differently than you probably would. There can still be a kind of connection and meaning, but only in the moment and it is not something you can depend on when vulnerable yourself.
In the end I think people are complex and their relationships are a power of ten more complex than they are. Because of this, it is not possible to depend on the consistency of any one person. Some are completely fleeting, some come and go, some are mostly consistent but might hurt you unexpectedly every now and again. It is a painful truth, but each person, including ourselves, are in the end more limited than we ideally hope to be.
The first man to raise a fist is the man who's run out of ideas. H.G. WELLS
The first principle is that you must not fool yourself, and you are the easiest person to fool. FEYNMAN If this is monkey pee, you're on your own.SCULLY