Oh mojobanana, your message broke my heart!! You sound so lovely, and I bet your girl adores you.
I know just how you feel-currently I am on my pwn (temporarily) with our Border Collie, and I feel so guilty that he is being left more frequently! :( By happy coincidence, a lovely doggy lady walks him for me and even lets him spend the afternoon at her house with her Springer girl. Also, our next door neighbours are lovely, and more than happy to help out. Take offers of help where you can: maybe try and arrange for someopne to walk your girl or spend some time with her when you are out, and in return walk their dog when you're free. Also the 'rent a dog' idea mentioned is brilliant!!
I think as long as you spend quality time each day with your dog (I speak generally, not directly at you!) then you are doing a great job as a dog owner, and I think you and her have a beautiful relationship :)
When we hadn't long had Jack we took him for a health check and the vet nurse was telling me that a man had brought a Collie in to the vet to be put down. He was 5, a beautifully-behaved dog who was perfectly healthy, he just didn't want a dog any more. Fortunately one of the staff was taking him home and finding him somewhere to live. Now THAT is irresponsible ownership!!
Love your dog and do the best you can for her, and you and her will have a lifetime of happiness. We are so fortunate to share our lives with dogs! :)
Cuddles to your little lady, Lisa and Jack xx