They stop talking
They stop showing one another basic courtesy and respect. Once that goes, they get too comfortable treating one another badly, and the relationship is more likely to fail.
They are not honest. I don't necessarily mean lies, but about who and what they are. When they want something, or they think something and they hold it in for fear of hurting each others feelings. Once that fear starts in, they stop talking.
Honesty about who you are is key to acceptance of your partner and for their acceptance of you. There are things you may not want them to know, but why?? Either they love you for you, or they do not.
Be honest with yourself, then be honest with your partner. The hurt (if any at all) of honesty is nothing compared to a broken heart.
Men never appreciate what they have until they lose it and women just get bored too easily.
This is why I don't believe in relationships.
They forget to be themselves and lie to their own heart.
hooking up with the wrong person