I could have typed your opening post, I can so relate. I think we are all in good company here -- everyone in this forum understands EXACTLY what this feels like.
I have this conversation with a friend of mine so often: WHY IS THIS SO HARD. We would ask each other this ALL THE TIME because neither of us could believe that managing our weight should be this hard. But it is. We finally had to stop pondering the WHY and start asking different questions about how we can cope, how we can make the best of it, what is right in our lives, how we can create new, healthy habits and strategies for sticking to them.
You CAN do this, we all CAN. Will it be the easiest thing in the wrold, I highly doubt it. But that doesn't mean it isn't doable.