I know this is incredibly hard. You have to step back. You have to stop telling her you love her. She knows that. By repeating it in light of her infidelity you are causing her to lose respect for you. Arguing tit for tat over who screws up is not going to help. She will just dig her heels in about being right herself. You are not going to win that fight. Take a look at yourself. Take a look at why your W feels the way she does. As hard as it is to do, try and validate what your wife is telling you. For example:
I understand you have been unhappy for a long time. I wouldn't ever want you to feel that way. How can I help you to feel better?
whatever she says, do it! Why? Because if you don't you're just providing resistance. I'm not saying agree to anything she wants but find a way to weed out the bits you don't agree with and validate any vague notions of unhappiness etc that she comes out with. You need to change your attitude with her. You need to start that change now!
I'm no expert. I'm only getting to grips with this myself now. This is just my advice
BD - 30TH JAN 2015 S - 30TH JAN 2015 PA CONFIRMED - 16TH FEB 2015 (SINCE AT LEAST OCT 2014) CONTINUAL TALK OF D ME: 31 W: 28 T: 10yrs M: 4.5yrs D:5, S:6