Any given relationship sprouting from coworking isn't terrible, but in aggregate, I think it warrants a decent amount of frowning.

At the worst it can be akin to nepotism which can quickly erode morale and productivity -- (there's no reason to work harder since the "fiance" will get the promotion).

At a previous company a manager dated her direct employee, and working in her team was really an awful experience because of it. Everyone knew it, and nobody could say anything for fear of retribution.