Being puzzled by another ly

Mentally, I am aware that not telling the truth is lying, too. But in the day to day life it is challenging. After finding an arrangement with my spouse to get out of my lying behavior, I tried to do my very best, following the "just for today" approach of the 12 steps. Today it happened again: my spouse discovered that I did not tell the truth in all the details on an issue, for which I promised to be honest. I MESSED IT UP AGAIN, and we ended in a dispute that made me feel very bad and sad. I have been working on step 4, compiling a comprehensive inventory, thinking that this would help to make progress. For today, I am just helpless.