Is this a sign of the changes in the tide?

I used to think it was me and I was just going crazy. Now I am really wondering if it is me or I am just too blind to realize what is right in front of me. I have been with the same woman for almost five years, but I have noticed some significant changes in her since the last year. She say's its me, and I don't feel it is or ever was. I mean I feel like I have been with her long enough to ask her serious relationship questions like what does she want in the long term from this relationship, what does she want out of life, what are her long term goals, I asked her one of what you would think would be the simplest questions to answer and that is, "What do you love about me?', and she either doesn't give me a straight answer or gives the, "Oh come on whay are you asking me that" answer which makes me feel empty. She is a bit controlling at times when it comes to certain things. I feel like she has a lot to hide while I am an open book. She seems to want to argue all the time and she sits on the computer more frequently now (facebook specifically) and I come home from work and she is there and I had to yell at her that the kids are into things so she will get up and do something. I ferel like she has been hanging out and talking to some of the wrong people who almost ruined our relationship before, and my best friend told me that I should be concerned about her agenda, because it seems like her agenda doesn't match mine. She is one of those people to walk around like she could nevber about anything wrong, and I am always the one to blame for the mistakes that I cause in our relationship. I have tried to save our relationship many times, because i do love her, but I think that its too late. It feels like I am going left and she is going right. It would be nice if we could meet in the middle. but I feel like there are so many things I don't know about her even at thins point that opening a can of worms would just make things worse. I have had people tell me I am wasting my time on a woman who will never change... I have people tell me that its only a matter of time... I have people tell me I need to move on..I feel like I have given all I have and then some to fight for our relationship to work... was the fight a losing battle?