This is how I feel too. I have been through the whole experience of feeling like a failure when I had to go 50/50 when nursing my son. It took me a while before I excepted that I just didn't have enough milk for him. Now looking back I'm proud that I managed to give him what milk I had for 8 months!is that however much breastmilk a mom can provide for her baby is important. The more the better, but every drop is important. I often get the sense that a lot of moms still think it's either breastfeeding or formula, one or the other, and if they feel like they've failed at breastfeeding then they have to give up and just do formula.
This time round with DD I had already decided that I would just accept what nature gives me and if it's to be 50/50 then so be it... she hasn't touched one drop of formula and it's been a year! Just goes to show!
I think we really need to focus on getting the idea of give your LO whatever amount of milk you have - it's better than no Mummies milk!