Try_hard
First before anyone comes to debate what I am going to say, I am going to clarify that it is my opinion, you understand my OPINION, for me it would be NTR for the simple fact that "another" Morty, I don't care if he is a clone with the same thoughts and soul or that they are connected either from the past or the future, the simple fact that "another" (whether or not a clone, I emphasize that I don't care) sleeps is ntr, although I am not going to leave the fanfic That's why, at least I'm going to feel uncomfortable because "someone else" slept with Morty's wife.
1) its not cheating since he is the same person, 2) its also not cheating, if mc somehow can divide hi thoughts to control Different bodies, then its not NTR, since they are jut bodies mc is controlling himself, unlike clones or shadow clones who have their own, soul/mind/personalities separated from mc while the hive mind idea its mc just using the bodies, his main soul/mind/personality is the one that controls all the bodies, that's the main difference between an Avatar and a clone, i have to spell like this because people here are stupid enough to not realize something so simple