Back to the original question - isn’t it true that most people meet their partners at work? I would guess that’s because people working together may have similar interests - plus that’s where you spend most of your time (esp if you are a lawyer in a city firm…)
I wouldn’t say it is ‘guaranteed to be a disaster’ - I know a lot of people that met partners at work. If you can be mature about it (both when things are good and when they are not so good) then I don’t see why you should feel there is an absolute bar on work relationships.