I think Tobias was too stuck in his ways (pardon the pun) to make any real investments on our girl Rachel.
I didn't really get a feel of Tobias being really supportive and caring, in a way a boyfriend would be, of Rachel spiralling into the bloodthirsty final days. She comes back from the Nice/Mean Rachel experience thing and he reverts it back to something about him, right at the end. She was on the edge and needing support during the 'leadership' decisions she had to make when Jake was away and he never really backed her. In The Return she asks him what's going on and all and Tobias tells her everyone is scared of her kinda thing and simply goes away. WTF, man.
Was there any attempt on his part during the final big arc?
All I saw really, was him, genuinely loving her, but never doing anything about it.
Lesson learnt, he loses her in the final book...