I tend to use the term when people reside together. But there is no art to the term boyfriend or partner, so it could really mean anything. When my partner and I moved in together, we probably moved to that term, even though our didn't share money as such (bought a house, but paid 50/50 and kept separate accounts) or have children.
As opposed to de facto which is defined.
I quite like the term partner. It doesn't come with the cultural baggage of husband. I cringe when people refer to my partner has my husband, which is often assumed now that we have a child.