Starstruck, firstly my sympathy and hugs go out to you. I truly know how you are feeling and how it is tearing you apart that you feel you broke your promise. But you didn't. You were with this old gentleman when he needed you the most, through all those times when he had no-one to care. You made his remaining time in this life worth living. At the very end very few are honestly aware of their surroundings anymore either due to their illness or medication. You held him in your heart and mind through to the end and he will know this.

Smile and be happy that he is now at peace and that you shared the time you did together.