Old woman ends up fucking her nephew, who caught her touching herself

This old fox, pretending to be a silly mature woman, spent a day moving from her husband’s bed to mine as if she were guided by sleepwalking as an excuse. As soon as I opened my eyes and saw her next to me naked and touching her pussy desperately as if she wanted to fuck me, I almost had a heart attack and fell out of bed from the shock. But when I observed her more closely, I still don’t understand very well why I started to get hard.