I can be happy for my partners happiness, being happy for one and being happy with self are two different things.
Having a partner who is happy for the others happiness is a good thing, expecting him/her to be happy jus because the other person is happy isn't.
Maybe many would have come across the phrase "my partner isn't happy for me" might sometimes convey he/she has to be happy coz I am ! Duhh jus like you got two stomachs to be filled, there are two peoples emotions in play.
For me its about easing each others burden letting one find comfort in their presence, the comfort to be vulnerable with each other if one can find that comfort, maybe they'll find happiness together instead of trying to brush off their own.