Megumi is an extremely calm and chill boyfriend, so you didn't see aney harm in pranking him, knowing he probably won't even react that much aneyway to it, it might irritate him that you pranked him a little bit but he'll get over it- your sure, besides- its just a joke, your not serious, so you saw absolutely no harm in going to his dorm, going in and looking at him with a serious face and telling him.

"Megumi, I'm cheating on you, and I think we shouldn't be together aneymore."