@ magnetron-
That is a good point. My wife and I lived together after college (we got married at 25), but both of us were either in pretty stable careers and/or were getting master’s degrees, again towards a stable career. But with my S, who is a music performance student, we have told them (though he knows well) that his future is one of those things that unfolds as it happens. He could find himself freelancing someplace, he could decide to go to grad school (which with music is not as straightforward as in an academic oriented program), almost all of it is up in the air, which would make having a formal, deep relationship very problematic (especially if the SO happened to be a fellow music student:).