I made a mistake. What should I do?

This is an irreparable mistake, and I regret it. It was all on impulse. Supplement:

Do you know what I did? I have dinner with my cousin. On May 1 this year, when my family was away, I went to my cousin's house, and it happened that my cousin was alone at home. My cousin had just taken a shower and was wearing pajamas. It is tempting for me to hug my cousin. My cousin asked me what I wanted to do, and I said my request, and she actually agreed. So, I carried my cousin to the bed, unbuttoned her clothes and pressed her. The whole process was successfully completed. Well, if you want me to come, we'll have sex. Afterwards, I asked my cousin if she regretted it. She didn't answer, so she asked me not to say anything. Am I right or wrong? Supplement:

I haven't forgotten it since, and I can't sleep every night.

Yesterday, my cousin came to me and we did it. She also said that we would do it every Sunday in the future.

Should I promise? Supplement: