A lot of great relationships go sour, you still remember the deep love that you had for this person and that's what keeps you together. The passion that you had for them in the beginning even though things aren't the same now. It's hard for you to let that feeling go and you keep trying to admit to yourself, through the constant fighting, that one day it will be that way again, but you're just in denial. There's a point where you have to realize that the two of you just weren't meant for eachother and this is what's making you a bad woman/man to the other, and you have to let go.
I also agree with fasterpussycat that it could be about a mistress as well.
A lot of great relationships go sour, you still remember the deep love that you had for this person and that's what keeps you together. The passion that you had for them in the beginning even though things aren't the same now. It's hard for you to let that feeling go and you keep trying to admit to yourself, through the constant fighting, that one day it will be that way again, but you're just in denial. There's a point where you have to realize that the two of you just weren't meant for eachother and this is what's making you a bad woman/man to the other, and you have to let go.
I also agree with fasterpussycat that it could be about a mistress as well.