My Dream Girl is my Sister

I'm Dwight 29 and live with my sister Shannon 26, our mother passed away 12 years ago and father passed away 7 years ago. He was 68 and mother was 49 at the time of her death (Heart failure). They married and had me and then Shannon and that strained our mother heart more she was advised no more children. Her heart didn't improve and she was on a transplant list but passed away before one came available. Shannon is petite as my father referred to her only 4'3" and shy with strangers. Both our parents were successful and we were left well off. Shannon had just finished university last year and as reward I took her away on holiday. We went to a island resort and had the same room, with the same surname on our passports everyone assumed we were married not brother and sister. Also I'm fairly well tanned and Shannon doesn't sunbathe as she gets badly sunburnt with very fair skin. I also take after my late father in looks and Shannon after our mother. So just looking at us you wouldn't pick we were siblings, I've had relationships and hadn't found my perfect match. Shannon didn't date as far as I knew at the time. Being with her all the time I started checking her out as they say and I liked I what saw. She might be short, but she was perfectly formed for her size and one evening she went swimming in a bikini and I got a instant hard-on looking her. This was a shock to me at the time, but I soon got over it. But from then on I was looking at her as a sexy woman and not as my little sister. I didn't make any advances towards her sexually, but looking at her as a sister was over. After our holiday we returned home and stayed close as was usual for us. I preferred being with Shannon then dating other women. At Christmas we went to a ski lodge and spent Christmas in the snow, the night before we returned home. We went to a party at the lodge and had a few drinks, not enough for me to get drunk. On returning to our room I gave Shannon a cuddle and I started to kiss and feel her up and we ended up in bed fucking and on our return home have slept together ever since. We don't take precautions and she isn't pregnant as yet.