I've seen how easily people change (particularly girls). How they compromise what they shouldn't (core values and that) but remain stubborn over the trivial things.
I've seen how needy someone gets because they're so deprived of love before the relationship and depend solely on the other half of the couple to fulfill their emotional needs - which is WAY too much responsibility and burden for one human. That person feels suffocated and bolts - leaving the needy one even worse off than before. More than heartbroken and so willing to take them back.
I've seen how two people can stay together no matter how life-draining and unhealthy it is. They don't try to make things better but won't leave out of fear of being alone. So they stay, get bitter, die inside every day, but hey, at least they're not in that loser "forever alone" group.
I've seen how one party give give gives and the other take take takes. That's a recipe for how to slow-cook a nice, big bowl of resentment.
I've seen how couples begin to take the other for granted and always assume that the other party understands them and thus never explain what they really mean - leading to frustration and arguments that don't even make sense to the other person because they're no Jean Grey or specialise in code communication or are just too lazy to try. Either way, communication breaks down and every conversation is a ticking bomb.
I've seen how mistrust makes people psycho.
As well as the need to control.
I've seen abusive relationships - both emotionally and physically. The "victim" stays and they leave only to return again.
I've seen all this and more.
I've seen people who've known this and believed they were the exceptions then fall into the same ole sob story.
Which makes me curious what I'd be like.