We're watching some of our most classic Bamon meta come to life before our eyes in these past few episodes: the concept that Bonnie and Damon are not accustomed to being anyone's first choice, and that if they were connected, they would be exactly that for each other.
With Bonnie, we saw it most dramatically in 6x05 when she sacrificed herself so that Damon could go home, so that he could be happy. It was an experience so new to him, that he's still completely in awe every time he talks about it:
With Damon, we're seeing it in action in the way he's prioritizing Bonnie over everyone else, even people who are important to him: compelling Alaric, refusing to indulge Elena's self-focus when Bonnie needs saving, feeling bad for letting Bonnie down rather than for what he did to Alaric, even right after getting punched.
Compare this to basically everyone else:
Jeremy, understandably or not, is prioritizing his own grief and well-being over Bonnie.
Elena gets some points for attendance, but the fact is that at every opportunity she was shifting the focus away from Bonnie... it was so blatant that I have to wonder if she went on this rescue mission just as much as a test of how she and Damon mesh together as to actually rescue her best friend. Again, prioritizing herself over Bonnie.
They went to great lengths to show us that Tyler prioritizes Liv over Bonnie.
And that Alaric prioritizes Jo over her.
I feel bad putting Caroline on this list since it's almost a plot contrivance she wasn't more involved, but the fact is that this wouldn't be the first time where Caroline prioritized boy drama over Bonnie.
I'm not assembling this list to demonize anyone on it, and I don't hate any of these characters for making the choices they made (other than Alaric, who I hate by default, sorry Alaric). But these are the people who Bonnie has prioritized over herself in the past. These are the people she has literally died for, over and over.
There's only one person she made that sacrifice for who was willing to do the exact same for her at the time. Only one person who proved with his actions that he holds her in the same kind of regard/importance: Damon.
This is the equality of their give and take. Of how they prioritize one another. This is how they demonstrate that they can trust that each will choose the other, when push comes to shove.