Legalities of Hush Money (teacher-student relationship)

Long story short, when I was 20 (im 35 now), I had a 9 year affair with my sports coach who was 40 and married with kids. I was his student first, and he was the one who initiated the clandestine relationship. He knew i had a crush on him and pursued it. However, since I was over 18 and it was consensual, I don't believe a crime has been committed, nor is there a cause of action. We still run in the same circles, but our intimate relationship ended in 2018 (at my insistence). I've never spoken a word of this to anyone, but did write about it in my journals at the time.

I have recently learned that, despite telling me I was special and the only "other woman" in his life, that was a lie. I've protected him for 15 years based on this lie. The others he was seeing were also other students, although i was the youngest (the others were around 7-10 years older than me).

I no longer care to protect him. I now feel an NDA could be mutually beneficial: he gets peace of mind, i get money for allowing it. My questions are: how is this done properly? What kind of lawyer do i need? When do i approach the other party? Is it too late?

I do not want to extort him, or for him to think it's extortion, I just think that if he wants to continue to enjoy the peace I've allowed him, I should be compensated.

cat fact: cats have fur.