It's not NTR if you aren't involved with them. Jill belongs with a guy like Rusty. He's a decent guy who has grown and wants someone serious.
And he can probably deal with her better than my MC ever will. Even if I ignore my dislike of Jill, she's not the brightest, and MC is a goddamn idiot. Stupid people should not breed.
Rusty is a nice counter to the naivete of Jill. He could guide her ti be better, not entirely unlike how Zoey helped the MC in the past. Surely nobody doubts Z is smarter than the MC.