What you need to do is what Jan originally suggested. At the halfway point of your stitches you will need to actually pinch the cord of the circular needle and pull it out between the two sets of stitches. If you can't picture how this would be done, take a look at the video on this page
called 'magic loop knitting' under small diameter circular knitting. For what you want to do, you won't actually be using magic loop knitting so don't let that confuse you - I'm just pointing you in that direction so that you can see how to pull the cable of the circular needle out between two stitches.
If you just have the stitches going in a loop around your circular needle like you show in your photo, as you bind stitches off the number of stitches left on the needle gets smaller and things get tighter and tighter around your needle and I can see how it would get more and more difficult. The above solution will fix it for you.