Because of the selfishness of things, what otherwise might be social creatures exhibit certain behaviors antithetical to common goals. The world of magic was no exception, in fact it was all the more harsh because magic can be addictive and those who crave it will stop at nothing to obtain it. Moreover, the more magic one obtains the more they invite a challenge, because magic has its own inertia.
The elves being both inherently magical and driven to cultivation inspired the rise of their civilization to dominance of their realm. A mirror gate granted them access to other realms which they could then learn about and dominate. Battle eventually gave way to diplomacy, but the empire crumbled from within when the most selfish rose to power and siphoned magic off those beneath them. Their petty wars with each other to gain more power, their selfishness bottle necking the scholarly process (that leads to greater innovation) by usurping cultivation, and their undermining of the truly gifted through early enslavement eroded the society until elves became almost extinct. The remaining survivors were only of mixed lineage descended of those who fled and those who were bred. Either way, wherever they escaped to they hid themselves understanding that if they were found they'd just be used as fodder for those who craved their magic. Eventually the knowledge of their society, including how to use the mirror gates faded into myth.
Oberon was always curious. He never craved power, but obtained and defended it to protect those he cared about. Having found and activating a mirror gate was initially out of that curiosity, but as threats grew to the Fae it also became a thing of power that he sought to master for the greater good.
Curiosity lent him to monitoring other dimensions through the gate. As threat was perceived it also became a defensive tactic. When he detected Zion he felt like he had stumbled on a magic mine. This creature has even potential to be the powerful asset he needed or a dangerous threat necessary to neutralize. Zion being mortally wounded left him with opportunity.
Fairies are a society of exchanges. Being curious creatures they like to trade, but being equally shrewd they are also tricksters. That trick has equal potential for help or hindrance.
Oberon produced a contract offering to heal Zion. What he asked for in return Zion still hasn't given. And what Zion didn't give Zion did take.
Some might think it's predatory to offer someone a contract on their life. Some also might see it as shameful to take an oath when you are deliberately trying to manipulate it for your own gains. But two shrewd and conniving tricksters conning each other seems pretty fair. It was even fairer still they'd fall in love.
The problem with being a con is the suspicion that it derives its strength from. Back up plans are effective exit strategies predicated on the assumption of being double crossed. Any good con has a tight number of them because planning well involves considering everything that might go wrong. Trust being often a crucial element in close relationships doesn't work well when one keeps their friends close and enemies closer, much less someone who assumes everyone a potential enemy. But that absent trust wasn't even what broke them apart.
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Lucky had calmed down significantly with the help of Cerberus. Upon exiting the woods she was able to shift back into her chipmunk form, but Cerberus still remained a wolf. She understood why this was. Having a dragon form lent her to considerable magical perception and knowledge that sometimes translated to her as a chipmunk though the exchange was dizzying very literally. It made her shift unstable, so the crossover was very limited. She did not suddenly have the magic of a dragon in her chipmunk form, she barely was able to stay in one shift.
This slow going with learning to control shifting was normal. In fact, the more powerful the magic, the more exponentially difficult it was to control. The best she could do right now was simply suppress her other form, otherwise the inability to harness its magic would inevitably degrade her into insanity.
When they reached the house Zion was there with Contessa. Zion, in typical Zion fashion, announced to Cerberus an upcoming jaunt to the palace. This enraged Cerberus and he began barking "You just casually announce you're going back to help the guy who cursed me after it taking this long to break it?"
"Well obviously not just me. I would have invited you, but I kind of figured since the whole curse thing you wouldn't be too keen on coming along." Zion said matter of factly.
"And he's going to forgive you for taking his wings why? Oh right, because you're helping him now and it's definitely not a trap." Cerberus's sarcasm overfloweth.
"I know what this looks like, but you should know me better." Zion said as they began magically packing.
"Knowing you is WHY I'm concerned. I trusted you the first time and what did that get me? A curse." Cerberus could barely contain his anger.
"Which I eventually broke for you." Zion retorted.
"You've got to be kidding me. Just when I think you've changed. My life isn't just something you can gamble with like you do yours. Not everyone wants to be undead like you." Cerberus seethed.
"Everything is a gamble, you just have to try your best to stack your odds. You know and I know there's no running here either and there's no going back. So we can either go at this half cocked or wait for it to come and be caught off guard. As some reassurance I do have an insurance policy." Zion's shadow held out a piece of amphibolite. Cerberus felt the strength of the magical item travel through him like electricity and passed out. He woke up in a bed in the palace of the Fae King.