I don't see asking for an immediate divorce as being too harsh if you are in an established and agreed upon monogamous relationship. Vows are not just words during a marriage ceremony. That is why I would be very careful in saying them.
Once the seed of "I am not enough for my partner" has been planted, it can't be erased in some people.
I see your point, Mono, and I do agree to an extent. Maybe it's my rose-tinted lenses that make me hope that anyone who has a strong relationship can talk about things or at least bring up a topic without the first response being "I want a divorce!" If that would be the honest response from the partner then there are other problems, communication being the major one. But this is of course just my opinion.