The only constant is change. Change is inevitable.
As we grow, as we age, we change.
How does promise factor into the equation then?
To me, a promise is a promise, it should always be kept and upheld, else it defeats the purpose of making a promise.
A promise shouldn't be something we discard or alter at whim just because it becomes inconvenient. It is exactly when things become tough or inconvenient that the strength to uphold a promise becomes paramount.
A relationship will only work if both sides uphold their promises, treat each other with respect, and not take the other for granted.
Repeated broken promises and disregard of the other feelings and needs will poison the relationship, turning it toxic.
Change in a relationship should be mutual, not individual. Unless of course, nurturing the relationship has never been part of the equation. My way or the highway. It's your issue if you don't like the changed me, there is no turning back, it's the new norm so get used to it.
When we are in an adverse situation, we try to change it. If we cannot change it, we try to change ourselves to accept it. If we cannot accept it because it simply adversely affects our wellbeing, making our life miserable, we leave.