JJ and I were in the same program and we met while in college. We had a lot of classes together since the college was small and we were getting the same degree. I never recall it causing a problem for me although he said in the warm months my legs were a distraction.
But that didn't harm his grades at all. Of course, we had classes together before we started dating too, so it wasn't a big deal when we did start dating.
I don't know I don't see it as an issue, in our situation anyway. But we also have worked in the same place for about 3 years and have no issues with that either, which most couples wouldn't survive. I'd say follow your insticts. You know yourself and your relationship better than us. If you think you can stand it and the relationship and and academic performance won't be affected then go for it.