this is probably going to seem like a strange, rambling metaphor, but go with it.
a relationship, any relationship, is like a bridge crossing a ravine.
a superficial or casual relationship means a shallower valley and a shorter bridge. a relationship that is deep and meaningful would be like a immense canyon, and the corresponding bridge would also need strong supports and lots of maintenance to sustain it.
the other thing i like about thinking of a relationship as a bridge is that in a good and healthy relationship, you have to meet in the middle of the bridge. if one person has to go all the way over to the other side constantly, they will begin to get tired or resentful for doing all the work in preserving the bridge. people need to work together if they're going to build something strong and stable.
the other thing that is true with relationships and bridges is that they both require constant work. both need regular upkeep. if you ignore the health of your relationship, it could crumble into the chasm it's meant to get you safely across.
but my most favorite thing about describing relationships like bridges is when there are fights. when you fight or disagree or argue, or whatever polite term you might use, it's like standing on your side of the bridge and yelling at the other person. and chances are they are standing on their side yelling at you. usually you don't understand half of what they're trying to tell you, and unless you try to meet in the middle and compromise, you'll never understand.
and sometimes it's true that relationships fail. bridges can crumble and fall. and sometimes you have to think long and hard about whether or not it is worth trying to rebuild.
and sometimes it is.