I will say, if you've read the author's previous work, he is not exactly making realistic romances. They are the sort of tropey, exaggerated and comedic relationships you only find in manga. Yeah, it doesn't really make sense but that's part of the fun. It is both outrageous and expected for her to have cutesy romantic moments with her assassin coworker who threatens to kill her at the drop of a hat. It is part of the bit. There's definitely better manga for the romance, so focus in on the comedy if the romance is getting on your nerves.