it is used for a couple whose relationship is reallllllllllly gooooood!

It is a kind of idiom, that Korean usually say when we see a couple with good relationship, caring for each other.  

And also, when you see your friend totally into her boyfriend/his girlfriend, you can say "깨소금이 쏟아지네" as well.

쏟아지다 is 'pour' in Engish literally, but here it means full of sth/abundant in sth, in a positive way. 

We also have another expression, "깨가 쏟아지다" which has same meaning with the one you mentioned. 

You looked perfect for each other.^^

You look so happy! 

아 그렇구나.. 이제 알겠어요. 정말 감사합니다!! 

페북에 어떤 사람 제 가족 사진을 그 표현 썼어요...