Firstly, it sounds more like you are just introverted. ADD is one of these "disorders" that gets diagnosed willy-nilly these days, when really, don't most people have a short attention span as a by-product of too many distractions and too much emphasis on entertainment in life? ADD people are usually more loud in social situations since they seek more attention than most others. It's possible you have been grossly misdiagnosed...it happens more than most people would care to think!
Introversion on the other hand isn't any sort of disorder or mental illness...though it is OFTEN misunderstood as one. It is actually a very normal temperment that just happens to be characterized by quietness, deep thought, introspection and other qualities that are frowned upon in this, mainly extroverted society!
Maybe do some research of your own into this. I can recommend a forum that is filled with mainly introverted type personalities. It's at
Marti Laney!
Maybe go there and see if you relate to any of the stories and things you read about.
Let me know the outcome and whether this has been helpful to you. It could be pivotal in being able to go into your original situation with these friends. It also sounds like there may be some co-dependency there...which you can also research about.
Hope this is helpful?