I've dabbled in writing and have looked at numerous writer guides to get better. One of the main tips is to show, not tell.
With SH, all they've shown during her romance is a slow burn romance throughout the game. Aside from some light flirting with other companions, she only shows serious interest in the player.
We simply haven't been shown anything different, outside of optional side stuff. People can engage in this side content or even headcanon all they want but the slow burn romance is the only thing that is truly canon if you romance SH. And unless the writing is changed, that's just how it is.
