To go back to something Marty said–let’s not forget who and what Tamara was: A driven agent for a cause, not a normal woman looking for love with her own insecurities and fears. If you think Hook’s pursuit is relentless, then Tamara’s was unavoidable.
The show made sure to tell us too that none of it was real for Tamara both when she says it to Neal and through the fact she confirms it to Greg in a scene where Neal isn’t there. The writers were not even subtle about showing us how fake that relationship was. They left no doubt.
Now I agree it might have been nice to hear more from Neal about such a huge betrayal, perhaps in a scene with Rumple about why he cannot trust him. Maybe they could have talked about Rumple having killed Milah, as they find Tamara’s body and Neal could have said he still didn’t want her to die, even if he hated the things she’d done. That could have been an interesting moment to show up their different instinctive reactions to betrayals. I’d have also liked it to lead into some discussion about Hook having run off with Milah and now Neals sort of facing the same worry. Then again, in the middle of rescuing Henry, on the run from Pan probably not the time they’d have discussed it anyway.
I feel like its never going to really get addressed though since when the story resumes a year has passed. There’ll be all these new things happening and like Graham’s death, or Belle’s incarceration it just won’t be relevant to the relationship between the characters in the face of new stresses.
“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass