it sounds like you have punished yourself enough about this and it is time to let it go. one of the aspects of sexual abuse is asking if the other party - in this case, your cat - was harmed by the event. it doesn't appear that they were harmed at all.

one of the aspects of youth is that we all have done things in that period of our lives that we regret. so the question is - did we learn from our mistake or have we continued to repeat our mistakes. frankly, it appears that you have learned from your mistake and, it's time to put it in its proper perspective. no one was harmed but a lesson is sexual appropriateness was learned. please stop punishing yourself.