You heard your SO saying as follows to a friend whilst out for dinner as two couples:
"Well you know after so many years it's just hard work".
Something about grass being greener.
"I have it all, money, nice home, business, so my doctor says depression could be to do with my relationship."
"I look out for number 1 now as xyz doesn't want to know"
In the context of having supported this person with their unmanaged MH (depression and borderline personality disorder) for 10+ years despite associated behaviours having a huge impact on your own life/ health.