There is zero nuance in a boss sleeping with someone who is a subordinate which is why every company very explicitly forbids it. Companies don't even allow people who are already married to be put in a situation like that.

Once one person has the ability to get the other fired, ruin their career, blackball them from the industry, etc. you can't know if they actually freely consented or not. Once you have coercive control over someone how could you even know that's not why they "consented?" Even if they initiated you can't know if at some point they wanted to stop but now felt they couldn't because of fear of retaliation.