This is a messed up ending. Noa quit her escort job presumably to take up the secretary job, did not bother to tell Amano, leaving the latter heartbroken. Why? For out-of-universe reasons, so that we can have "the reveal" at the end. In-universe, it makes sense only if Noa is a colossal sadist.
Plus, this just puts them in an even more awkward position, now that Amano is literally her boss. Dating people whose continued employment depends upon you is one of the worst decisions you could make in this regard.
I don't think it's quite that bad. It's not unheard of to date your boss, it'll just change the work dynamic, and since they already know each other beforehand they avoid overcoming the initial power gap. A lot of machine shops I've worked at or interacted with have the husband as the CEO and the wife as the secretary/front desk person, which the employment part was the least of the issues in those situations but it still worked out just fine. For them. The shop at large, maybe not so much. Fiction-wise, I think the expectation is they'll treat each other as equals or work it out like Zhu Li and Varrick in Korra.
I personally like to try to pull off surprises like this for/on people, although maybe with a bit more tact. We won't know because of how sparse the ending is, but Noa could have all sorts of reasons for doing this from proving she could get the job on her own to avoiding accusations of nepotism to thinking it could help or teach Amano something. All in all, way too rushed to have a fulfilling end though