(idiomatic, mostly used conditionally) in someone's situation.

Fully available to help or to be of use to someone, or some organisation. / (formal) By way of introduction on first meeting another person.

For someone's sake. / According to someone's interpretation or account.

(idiomatic, derogatory) Receiving money from, and under the influence of, a person or group of people, with the expectation that a favour or advantage will be proffered in return.

(idiomatic) Preoccupying someone; present in someone's thoughts.

(idiomatic) Available to be used at any time and in any way the user sees fit.

Very grateful for something (a favor) that someone has done for one.

Blocking someone's light, especially when someone is attempting to see a particular thing.

Synonym of in someone's shoes

(idiomatic) At the monetary expense of the person indicated.