I think the best headspace to be in when you begin a long term relationship is that you are responsible for your own happiness and you are otherwise happy/fulfilled on your own.

Expecting someone to make you happy means that you are not happy on your own, which means you have baggage to sort out. Having unsorted baggage is often a recipe for disaster.

Now, when i say "it's not my" job" to make my partner happy", I don't say that i should not care how she (or he if you are a woman) feels, whether they are happy or not, i should not listen to her, should not help her, or should not put in any effort to improve our emotional life. What i am saying is that no one should put in extra effort for a prolonged amount of time if their significant other is not willing to do it for themselves. In that case all that effort does is enabling his/her behavior that resulted in their unhappiness in the first place, which is not "help", but rather the opposite, merely perpetuates the problem and drains people dry in all regards (this by the way applies to any relationship between people from friendship to kinship IMO). No one is responsible for anyone's happiness, we are all responsible for our own and the best thing we can do to others is to be happy on our own.