I feel torn. Ideally, I just want the girls to graduate and be happy, and sensei finding someone his own age. He's already crossed a line with all three of them, even if it came with invitation, for his sake and their's he should step back and reaffirm their relationship as teacher and guardian.
At the same time, the isekai protagonist in me says smash all three. The duality of man.
Come to think of it, I feel like his own personal life isn't really fleshed out enough, even with the reveal of his families' death. Sensei needs love too I feel, hopefully he gets it from an equal.