Is there any way to deal with guilt.........?

hate so many regrets but I feel especially guilty how can I forgive myself for doing this? I feel really bad about some of my teenage behaviour. Even tho Im 23 now, I felt lke a compltelty different person when I was a teenager and when I was 14 I sniffed my sister's undies and toucher her v*gina when she was asleep. I know its ewwwww. I feel really guilty now and dont know what would possess me to do that. Perhaps it was curiousity or something but all Im left with is guilt and dont know how to forget about it. I dont wanna ruin things between my sister now cos we are good friends. Im 23 but thinik I need a girlfriend or soemthing?