You can't stop feelings, it's a total pain.

Why would it be inconvenient for them? And it's not really a matter of taboo as much as your comfort level. Since you know the budding feelings might not develop, and there's already something there with someone else. But if you feel too guilty, it genuinely might not be worth it.

I'm against the whole "forgetting" thing though. In my experience it's just a hassle and prolongs the inevitable.