There are always signs, but we seem to see them only in hindsight. Why is that?
Breaking up is hard to do, I agree, and just as with romantic relationships the break-up can sting.
A friendship in a downward spiral can be as difficult to deal with as a cheating boyfriend.
When the relationship is on a downhill slide, your sense of self will suffer at that hands of a gossiping, disloyal friend.
I am sorry to hear that you are going through this.