I have a boss who I feel is taking sides with another co-worker?

The co-worker got an attitude with me, then told me if I didn't want to work with her that was fine, I never said that I didn't want to work with her. I then went up to the manager who said that maybe I did get an attitude with her, but he didn't know the whole story. I confronted him and told him he was taking sides. The manager then went on to say that I am hard to work with, meanwhile I am quiet and keep out of people's way. Later, the manager came to me and said that maybe the other lady did have an attitude etc.(I think he was doing this to downplay the situation or cover his tracks) he went back to the lady said something to her then started laughing. Was this boss really taking sides or am I over reacting? How do I respond if this co-worker keeps up the bad attitude?