I am 26, she is 23. My mum married her dad 10 years ago and we got on from the moment we first met. She lived with her mum and we only met at birthdays and Christmas, then two years ago she finished school and got a job near where we live, so she came to stay with us.
My girlfriend and I have been dating for three years and everyone thinks we are going to get married and settle down soon. I thought so too until a few months ago.
Mum and my step-dad went away for the weekend when my girlfriend was at her sister's party, so my stepsister and I were alone in the house.
We had a bottle of wine and watched a movie snuggled up together on the settee. It felt so comfortable, we turned to each other and kissed to say good night, but the kiss was electric.
Suddenly we were all over one another. It got very passionate and in the end we went upstairs and made love. It felt so natural and so right.
We expected to feel regrets in the morning but we had a wonderful day together, making love and acting like a real couple. Our relationship has carried on since though I've been feeling more and more uneasy about deceiving my girlfriend.
We decided we should tell my mum and her dad last week. We hoped they would be understanding and help us decide what to do but they were both very angry. They say unless we finish they will throw me out and tell my girlfriend.
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