It's always negotiations?

I hate my relationship. Sometimes its good, but most of the time it sucks. I work 15-18 hr days, 5-6 days a week, and I am always apprehensive about coming home. I never know what to expect. Will she be in a nice, happy mood, or will she be like, "hello, how was your day, kiss, good night"? I feel like there's no pion, no romance. Her moods range from light to dark on any given day, or morning, afternoon, night. It's so erratic. I've done all I can, I feel, to deal with this, going so far as to checking myself into counseling thinking that it's me with the problem. I have worked so hard to salvage this relatioship, because, during those moments when she's light and happy, which are rare, I fall in love with her all over again and really want to stay and work it out. It's during those dark times, when I feel most unloved, unwanted that I want to leave. She must know how she makes me feel. It hurts. I want to be there for her, I want to love her, but she makes it so hard to stay. Help