I think it comes down to respect for yourself and for one another. If you love and repsect the other, you will do nice things for them, to help them or make them feel special--anything short of smothering behavior.

But then, up until almost the day she died, Grandma always fixed Grandpa's plate for him, cut his meat, the whole shot. I've let my SOs know that I'm a big boy and capable of doing for myself.

Hopefully when you or the other do something out of the ordinary to show your love and respect it's seen as that, not just as something that is expected because of some sort of social dictum.