When I was first learning about psychoanalysis someone told me, "psychoanalysis can be described in lots of different ways, but I think that fundamentally it is the examination and description of the relationship between the subject and their object."
Frued used the concept of libido to describe the emotional investment people (i.e., subjects) have in particular objects. An "object" can be lots of different things, a person, an experience, an ideology, so on and so forth.
Lacan added to Freud's theory of libido by explaining how the presence of the libidinally invested object creates jouissance --a sensation (i.e., affect) of excitement that is felt in the body.
Libidinal (emotional) investment --—> Object --—> Sensation of Jouissance
Something important to keep in mind when dealing with libidinally invested objects: The sensation of jouissance is addictive! We are all addicts. We are all addicted to whatever it is that gives us a sense of satisfying excitement.
Just as much as having the object makes us feel good, not having it makes us feel awful. The absence of the libidinally invested object creates an affect of frustration. Having whatever feeds our addiction to jouissance makes us feel great, but the absence of this object (i.e., the absence of what gets us high on jouisance) creates a feeling of withdrawal.
What satisfies us can also frustrate us. This is a structural thing, and it can't be any other way.