You may be expecting too much too soon from yourself, whereas you may not be ready for all the drastic changes. Implement lifestyle changes progressively and incrementally instead of big-bang tactics. This is a much more sustainable way for you to persist than going cold turkey, and you should acknowledge it whenever you feel guilty.
On the other hand, you should also praise any effort, however small, you make towards your greener lifestyle. Look back at where you were and where you are going and pat yourself on the shoulder for the progress.