When I first got to the Realm of Light, I didn't care about it at all. Zant could've covered the entire realm in twilight and wouldn't have cared. All I cared about was returning to my true form by defeating him.
When Link transformed, proving he was the hero of prophecy, my only thought was "oh, I can use him."
That was my thought process for the entire time of both Faron and Eldin. It wasn't until Lanayru when I started to actually care about the Realm of Light and its denizens.
My plan changed slightly to get my true body back and to protect both realms. Then, when I found the broken mirror, Link and I had to go to Snowpeak. When I saw what a quarter of the mirror could do to someone. I realized that the artifacts of my realm were too terrible to keep around.
Fast forward to as I'm saying my (fake) goodbyes to Link and Zelda. Zelda suggested that we keep the mirror intact so we could travel between our realms. But... I knew what had to be done. My people's artifacts had damaged the Realm of Light. So... I shattered the mirror, forever separating our realms.
A difficult decision for me as I had to also choose: my people or staying with the person I grew to love. I chose Link. My people would've voted for a new leader after another 9 years anyway. I was only to rule for a decade, just like the previous leader and the one before and so on.