Who said anything about that? You can share your emotions with your partner in a way where you don't expect them to be your personal therapist. Generally, it's healthy to have a support network, preferably not just one person and especially not just one person who isn't even a professional.

When you share your feelings with a therapist, that exchange is in one direction, you should never have to emotionally support your therapist. That is however not how it should be with a partner, in a romantic relationship both people should be able to share their emotions and receive support, and that isn't possible if one person is treating the other as if they were a therapist and not giving them the space to share their emotions in turn.

Most things in life are about balance, just because you don't agree with something all the way one side (e.g. there is no way to create an unhealthy relationship dynamic by sharing your emotions, regardless of how you do it) doesn't mean that you agree with something all the way to the other side (i.e. you shouldn't give two shits about your partner's emotional well-being).