I wouldn't be so sure about that. Masuda Eiji's biggest hit before this one, Jitsu wa Watashi wa, spent the majority of its run with the main couple as, well, a couple. The confession and them getting together was far from the end. Admittedly, the scope of this story is much smaller, so it probably can't go on as long as Jitsu wa, but I'd think it can still go beyond confession into dating.
No, see, there's four of you, which is a great number for a group surveillance team. Each person drifts in and out regularly, so the target doesn't keep seeing the same tail for the full duration.