I fell into it again

A few minutes ago I just fell in and even before that my dad walked in leaving and saying goodbye because he had to go to work. It made me feel terrible that I would think of doing something like that. I am a Christian and I should know better but the urges are just so strong. I promised to God I wouldn’t do it again and guess what, I did and thought about him before during after doing it. The guilt weighs my heart down. What do I do? Please any tips I don’t wanna be a part of this sin anymore.