This question already has an answer here:
Let's say I am in a committed relationship with a woman, but we are not married; talking about her as "my girlfriend" seems a bit silly, as it conveys the idea of something juvenile, and 1) our relationship is serious and stable and 2) while she's not old, she is definitely not a "girl" anymore.
However, we are not married, thus "my wife" would be an exaggeration; "my woman" could do, but I don't really like it, as it seems to imply an idea of possession rather than companionship. There also are "companion" and "partner", but they don't necessarily mean a romantic relationship. And, of course, "lover" seems more appropriate for a sex affair than a stable relation.
What is the right word to use here?
Also, the inverse variant (being in a committed relationship with a man who is not your husband, and calling him your "boyfriend" doesn't seem right).