Fixation

[Dave Paprocki]

The act of uniting chemically with a solid substance or
in a solid form; reduction to a non-volatile condition; -- said of
gaseous elements.

[Dave Paprocki]

When you are [obsessed] with somebody or you are concentrating [like crazy] on them. This is not always good, though, as you might not be able [to be with] the person, or they might not like you in the same way.

[Magaret]

mentally:when a person is obsessed with another person, inatimate object,or animal
visually: [staring] at or [gazing] at something or in a constant [direction] for a long time

[Cami]

An obsessive interest in or feeling about someone or something.