I honestly wouldn't have minded who Ian would choose in the end, but in terms of the plot/story, it made more sense for me that he chose TJ.
I know a lot wanted Jo for the end game but he actually has a bright future ahead of him, I didn't like how he was slowly coming to the dark side when he was with Ian. Their love was real but just not meant to be.
The author did a great job with the love triangle. When readers are divded on who should be the end game, that's how exactly it shoild be.
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So this is basically esper and guide plot but they just used different terms which is ikigami and donor.