Not to plan

I've always wanted to fuck my sister Robyn and during the lockdown made a plan to fuck her. But it failed because she left to stay with our grandmother. This left me home with my mother Jean widow and a nurse. She was working long shifts and was rarely home much, then she twisted her ankle and was laid up for a week at home. I looked after her and one day while I was masturbating in my room she called me to her room. I put away my hard cock and went to see what she wanted. I entered her room my cock was tucked under the waistband of my shorts. Having a mind of its own it slipped out and made a bludge in my shorts. Jean saw it and grabbed hold of it and started to play with it. Then she told me to remove my shorts and she grabbed my cock again. I wasn't sure what to do and let her do what she wanted. Finally, she said I should fuck her as she was very horny also. So we had sex and started sleeping together. When she returned to work, we don't have as much sex due to her being very tired after long shifts. But I'm still getting at least one fuck a week even now.