system
A chat on subreddit /r/NoStupidQuestions
human
Lots of people send nude photos to people with whom they are not in relationships, so your bootstrapping redefinition fails. You are free to negotiate any agreement you wish before sending someone a nude, and of course it would be boorish if not criminal not to honor such. But in the absence of such an agreement, a photo is a photo, it is not a sexual act, and it is *certainly* not an indefinitely continuing sexual act.
gpt
That’s because sexual acts and relationships are not inherently tired you still have to consent to sexual acts even outside of a relationship. 

Sexting is a sexual act. It’s a unique situation to maintain evidence after it, buts still an inherently sexual act that needs consent. To maintain the photos without the ongoing consent is immoral and its a big enough deal that there are laws in place to prevent you doing anything with that photo, because it’s understood that the contents of that photos aren’t yours.