My experience in grad school has been that almost all relationships between grad students in the same department have ended well**. So from my perspective, it's not just that something occasionally works. Instead, I would say that the really bad breakups where there is lasting drama/conflict and awkwardness is pretty rare. I can only recall one instance out of the 20-30 relationships I know of.
** To clarify, when I say "end well", I don't mean that they ended with the students married to each other. Sometimes a relationship is just meant to try something out and if it doesn't work, both parties move on to other things. Ending well just means that the relationship ends but both parties can still interact with each other as professionals. Maybe there are a few weeks of initial awkwardness between both parties and their social circles but if it fades with time, then it's fine. Also, maybe if the two students were friends before but are no longer friends after the relationship ends, that's fine too. The whole department doesn't have to be friends with each other!
At one point, there was a department I know that had about 25 grad students and I think there were 5 or 6 couples within the department (i.e. almost half of the students were dating or married to each other). I think it was a fluke though, people graduated and the density of couples dropped soon after.
(Although I wonder if there is significant confirmation bias happening here. Do I not remember the bad breakups because I suppress bad memories? Or do people remember the dramatic endings/breakups more than the relationships that just fizzled out? Probably some of both?)
