familiar / used to; accustomed to / in a (romantic) relationship with

habit

familiar; acquainted (for long)

to be acquainted (with each other)

familiar; known

(colloquial) to acquire the (bad) habit of

an acquaintance (person)

(transitive) to be(come) acquainted with someone; to meet and speak to someone for the first time / (transitive) to make or become familiar with something

to lapse back into one's old ways; to relapse into vice