The funny part: casarse comes from the common Spanish word for “house”, casa. That makes sense: getting married is fundamentally about two people building a house together, metaphorically and literally.
In English, although marry is unrelated, two English words convey the same concept. Husband, in English, comes from the Old English “hus – bondi”, which mean, “House Dweller”: so the Husband is the one who lives in the house!
Even better: American slang hands down to us a lower version of the same concept, the slang phrase, “to shack up”, meaning, well, to either live together in sin — premaritally — or more recently, to have sex in a one-night stand. A shack, after all, is just a poor house.