Re: was it my mistake?
In life, you're bound to meet all types of people. Friends argue and fight too, it's healthy - as is a bit of introspection. Sometimes misunderstandings happen, other times, people are just not what you might have thought them to be.
Don't allow the self blame to take over your life. Look into the situation, and analyze your own actions. If there are some corrections that can be made from your side, those need to be addressed first. Then you need to be upfront and honest with the friends in question. Once you're all able to communicate, you will know if you want them in your life or not. If they really are not people of quality, then you are most definately better off without them.