I believe you're thinking of Acting Lessons, when you help Liam hook up with the Smurf (whose name escapes me) who is a possible love interest you can choose to end with. But you can't hook Liam up with her if you pursued her as a LI, only if you rejected her at the beginning of her route.
And the definition of NTR in F95 terms, as it was explained to me anyways, is your LI cheating on you for the express purpose of creating jealousy in you, the MC. By that definition the flashback/nightmare scenes are most definitely not NTR.