When will chase know that josh is his omega or that he is an omega in the novel?

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Chase will find out near the end of the main story, like when ~6/7 of the story it done. And it's not that there were not enough clues there before, because those clues were there, but Chase was oblivious, ignored them and believed Josh's excuses, kind of all of it.^^
When he found out there was no other option than that Josh was an omega.^^"
Most other alphas would have known much earlier with the information Chase had.lol