I saw my son fucking my mother

I'm Janet 39 divorced and live with my mother Caroline 57 and my son Paul 19. I work shifts at the local hospital in reception and back in February I came after working a shift and saw Paul thru a window fucking his grandmother Caroline. Normally I would drive into the driveway, but this day I had dropped my car off for a service and they had dropped back home. So Paul and Caroline didn't hear me pull up and so I saw them fucking. At first I was angry and was going have go at both of them. But as I reached the front my anger subsided and then I had a feeling of being jealous that Caroline was getting sex and I wasn't. We're not the hottest looking people all overweight and plain at best. I decided to let it pass and keep quiet about seeing them. I went to the driveway and made a noise to let them know I was home before entering the house. On entering Paul was sitting reading a book that was upside down and Caroline wasn't in sight. Shortly after I entered she came out finishing dressing to go to work and shortly after she left. I made some small talk about nothing in particular and then went for a shower. Paul had the day off and while showering I noticed him watching me shower in the mirror. This turned me on a bit and so I started to play with myself. I saw Paul start to play with himself by the reflection in the mirror. So I decided to catch him watching me and he was caught pants down cock in hand. He was totally shocked at being caught and I told him if he like to watch me play myself while he played with himself. He shouldn't fucking me to satisfy the both of us and grabbed his arm and took him to my bed. Paul fucked twice that day and took me to pickup my car. That was the start of our sexual relationship and after a week I was able to catch both Paul and Caroline fucking and joined them. That's how it is now and Paul even fuck either of us in full view of the other.