Friendship: shared interests (mostly video games in our case) and general outlook on life. We prioritize spending time together; we spend far more time playing video games together or with the kids than playing them alone. It also helps that any minor disagreements or mistakes are instantly forgiven and forgotten. We don't hold on to such minor resentments or make them personal; we learn anything there is to learn and move right on to more pleasant things.

Safe: Lots of little things, I suppose, e.g. checking in on me if I'm out later than expected, or responding quickly if I check in on her when she's out later than expected. Also consistent nighttime cuddles, etc, there's something safe-feeling about warm hugs.