Prudence should have counseled that lawyer to demonstrate more prudence. Dating a junior employee of the company where you work is fraught with potential pitfalls, even if not contrary to company policy. But leaving that aside, he brings too much of his personal life to the office if Sara already knew all about his relationship history and "everything else" through office "gossip."

Unless Mr. P/Q is a celebrity whose life is under scrutiny by the tabloids, the only way his office knows about, e.g.,the extensive nature of his ex-wife's cheating on him while married, and the fact that it took him "many, many, many months" to recover from her infidelity, is because he's been blabbing about those at work. I recommend he knock it off. It's perceived as an indication of poor judgment/lack of discretion, traits no employer wants to see in its legal staff.

I thought the letter implied that the 20-year-old's position was temporary, and now that summer is over she is no longer employed by his firm and is back at school. That eliminates the junior/senior employee issue, as long as she has no intentions of applying for a permanent position there when she graduates. Might be a good idea for him to just make sure she's aware of that, since she's young and might not realize it.

As for your suggestion that he be more discreet about his personal life at work, by all means. Especially if he intends to date someone he met when he was the senior employee and she was more junior. People could well assume that the romantic relationship began before she left, and while he needed be required to date stealthily to remove all possibility of the appearance of impropriety, keeping his mouth shut here would be wise.