Also - ask her to compliment you more.
I had an ex who got very unhappy in our relationship, because at that point in my life I was neither a very affectionate or positive person. I didn't go around putting ice cubes down his shirt or telling him he looked boring, but I was hardly warm and sunny.
I could tell he was unhappy, and since I loved him that made me unhappy, and when I'm unhappy I withdraw - and things got worse.
Eventually he told me what was wrong - that there wasn't enough non-sexual physical contact, that he felt like I didn't find him very attractive, and that I wasn't really appreciative of him.
I felt terrible, because I could totally understand why he would feel that way. I had to work to change. I had to remind myself on regular to find something I liked about his apprentice and tell him I thought it was cute. I had to remind myself to sit close to him when we watched tv and snuggle into his chest and maybe put my legs over his lap. I made it a point to always tell him how happy I was to see him when we got together for a date or something. It did not come naturally at first. It took a lot of practice. When I looked at him, I did not think 'Damn, his butt looks cute in those jeans.' I thought 'Oh shit, I need to say something nice. What's nice? His hair looks good today. But I told him that this morning. Um, oh, his butt! I love his butt!'
'Great ass, honey!'(facepalm)
Seriously, it's work. You have to force yourself into this habit that does not come naturally to you, and at first it just feels forced and weird and you feel like a phony jerk (even though you mean the compliments). But now, it is natural. With lots of concentration and practice, I have trained myself to be a mushy romantic.
One of the biggest things that helped me through it. When I said something nice or hugged him from behind or told him I was glad to be together, he gave me a hug and said thank you and how much it meant to him. And that made up for the weirdness of it, so I didn't feel more awkward about doing it again the next time.
Also, I know this is tacky, but 'When you _, I feel _.' statements are really useful. Also, avoid the words 'always' and 'never'.