My Ex GF used to give me footjobs - with "happy accidents"

My former GF, let us call her Jade, used to give me footjobs almost daily. She loved it and for her it was a funny game that required coordination and additionally she had her feet massages by my cock - at least that was the story she told me. Nevertheless I didn't complain nor questioned her story in any way.

One day she started to increase the amplitude of her strokes as she was sitting in between my spread legs and thus hitting my balls with her heels as she did the footjob. It did not hurt, but she started doing it. Weeks have passed as I realized that this heel-on-balls kicking increased not only in duration but also on intensity. She sometimes "slipped" with her feet and kicked my balls with her toes. I could see her laugh and it was fun for me - it was the first time I felt a kick to my balls and it was really nice. I liked it. So I didn't say anything.

After some times she started rubbing her heels in my balls kicking them while stroking my cock with her toes only. And one time she made me cum with her feet again only to "slip" right at that moment when I came to kick my balls pretty hard. I came like a fountain and she laughed about it. My balls really hurt and I felt humiliated.

I remember her saying "that made you cuuum... wow, I should try that everytime"

And so she did.
She started to kick my balls more and more often, more and more frequent and more and more intense.
Sometimes she started a footjob by kicking my balls for 20 minutes before letting me cum.

Note that I never said "I like this" she just went for it and had her pleasure.

As she moved away, far away - we split a year and a half ago. I sometimes write her messages and we are still in contact.

I am from northern Germany - so I hope my english skills were enough to portrait this story in sufficient detail and I apologize for any mistakes in langauge I made.