A bit of fun

Bored and nothing to do and only my sister home that weekend. Our parents were away at interstate lodge meeting of my father's lodge. I decided to go swimming in the pond outback of the barn. But wasn't up to walking back to the house to get my towel or swimsuit. Deciding to go in naked. My sister saw me swimming and came over and asked how the water was. I said great, she could see I wasn't wearing anything and decided to join me in the pond and also came in naked. We played around in the water for a time and then I just kissed her, and she kissed me back. Then we started fondling each other and left the pond and entered the barn and had sex. That night we slept together and have started having sex regularly since. My sister takes precautions and hasn't gotten pregnant, we both have partners and regularly have sex with them. But fucking my sister started as a bit of fun and now is obsession between us. We can't seem to break the need to have sex with each other. But we aren't trying very hard either.