Its a personal taste, in my experience i've seen too much nuclear waste after people break up. Even friendships can be quite bad. As an example i knew 2 guys who were friends pre-work, one invited the other and they had one of the most toxic relationship.
There is difference between work and outside life. Working people have different ethics for example i might like to concentrate on achieving my goals and finishing work faster while the other might do the opposite or hold different priorities. While we are work-strangers we don't try to dictate or hold expectations from other people.
I know very well that work-place romance is EASY, i was working with some women more than i was interacting with my family or friends (time wise). And somehow "romance" started to bud. Was it really romance? After introspection i realised it's just a basic psychological bias we humans have i.e. close proximity.
Usually if you work closely with someone for a long time you develop feelings for them be it romantic or friendship.
P.S. Work place infidelity happens exactly because of that, you are forced to share more time with your work partner than your actual life partner and some animals confuse it with new "love". Mangas case of course is different since she decided to work there in order to be closer to him.