Aren't you so thankful that His faithfulness isn't dependent on our actions?
One thing that has really stood out to me when reading the Word is that God consistently uses imperfect people for His glory.
Even the "greats" of scripture - David, Abraham, Jacob, Noah...etc...all had Biblically recorded flaws.
God still used them. He was still faithful, even though they were broken.
Genesis 8:21 says in part "the inclination of the human heart is evil from youth onward." - We all sin and continue to sin despite our best efforts.
But, just like the examples in the Bible, God is still faithful to us.
Satan wants us to only see our flaws and wallow in that.
God says, "I see you, and I"ll use you for my glory."