Right now Rey is one confused soul. He's jumping from big ego Rey...to rude Rey...and then to insulting Rey. Of course the passionate Rey makes a special appearance but then it's back to square one! The thing with him right now is that he simply does not know what he is doing! He has no control over himself and is unable to keep his emotions in check. He's all over the place.
The question does arise - did Rey take Taani for granted? I would say yes. In Taani he found a staunch supporter, someone who had blind faith in him. She held him in high regard and he protected her like she was the most precious jewel in the whole world. But Taani gets promoted, holds the position of GS and Rey sees red. He just cannot handle it. He thought she would always be the girl that he could mould into according to his mood.
But as you rightly mentioned, Taani has always been loyal towards Rey. She has always had his best interest at heart. But he does not see it. He is blinded by anger and is surrounded by tall walls of misunderstandings which he has mostly created. I don't think he has ever stopped to think even once about Taani's true intentions. He has thrown insults and has undermined her on numerous occasions. But as Taani once told him correctly, she has come infront of him as Taani and NOT GS many times, but he failed to see that girl.
It clearly seems as though Rey is in a tug of war with his inner feelings. He loves Taani and it pains him to be apart from her. But at the same time he keeps pushing her away. Why? Perhaps it's easier for him to remain indenial. But although this may work for a short period of time, it is beginning to catch up on him. It's now coming to the point where everything is becoming unbearable for him. And in Wednesday's epi we saw him lose complete focus and at one point he had his head in his hands. That is the impact of Taani on him!
Ultimately Rey isn't really fighting with Taani...he's fighting with himself, with his feelings. Accepting his feelings is hard. But to keep Taani away is proving to be even harder!