Is it normal to make secret sibling pacts

Ok My Sister and I are 3 years apart We Started fooling around together when we were Young playing little kiddie games like Truth or Dare, Doctor, Show and Tell, And Grown ups. One day in our mid teens My sister and I were in our basement playing truth or dare with some friends when her friend dared My sister and I to try position 69 on eachother. After some teasing my sister climbed on top of me and pulled my pants and boxers down. I pushed her skirt up and pealed her panties off as she took me into her mouth. Our mother came walking down the stairs to find me and my sister performing Oral sex on eachother while some of our friends were also performing oral on eachother and masturbating while watching me and my sister. We all were in huge trouble. Mom called some parents and grounded us. Afterwards we were told not to play with those kids again. We were also told what we were doing was forbidden and bad not accepted by Law, God , And society.
But it never really stopped us, It just excited us more. 2 weeks later while we were home together grounded We snuck off into the garage and started giving eachother oral. A month later while we were home alone grounded on a friday night we tryed Intercorse.

2 months later If we were stealing condoms from our older brother and having sex whenever we could get away with it. We dated others through Highschool but continued having sex together Secretly. We called it practice. Before I went away to college We made a Pact, To practice Together when we were Single. Its been about 6 months sence I've seen her last but we have held up to that pact Has anyone ever made a Pact like this before ?