When in a relationship or partnership, we may accidentally subsume the other's being - especially when in public.
When in public, you may think you need to present a united front, and that private issues are meant to be privately discussed. This leads to thinking that there needs to be a 'public persona' of the relationship.
While this makes sense for the discussion of sensitive issues, it shouldn't change the nature of the relationship between the two people. Which is always mindful of the independence and respect due to each other.
By acting as if you need to present a united persona, one of you may accidentally ignore the other entirely. You start to act as you always would - ignoring previous agreements. For example, you may have agreed to refrain from saying a certain phrase, but then in this 'public' mindset you forget about it.
This means you stop treating your partner seriously all the time, under the excuse of being in public. You disregard ongoing agreements and behavioural modifications (that you should have kept working on).
What's more, you end up not seeing your partner as an independent individual. Assuming a joint public persona means you assume the behaviours of your partner.
You stop working for them and treating them as independent individuals.
Individuals who can leave at any time, who have a right to be angry, and who do not have any obligation to act as you expect them to.