Is it right to use this expression regarding relationship between people?
I saw this expression with regard to political affairs can I use it to
describe a relationship between two people when only one of them
keeps in touch?
You're correct; a unilateral relationship is typically used in a diplomatic or political context. One party attempts to reach a consensus with the other while the other party refuses to cooperate. I witness this phenomenom in American politics on news broadcasts where President Obama constantly tries to confer with opposition Republicans, yet the Republican leadership behaves like petulant children, opposing him solely because of who he is. Hence, President Obama has a unilateral relationship with Republicans in Congress (the US legislature).
In a more informal, everyday manner, I prefer to use the term one-sided relationship to describe a relationship where one party does all the contacting.