You might start relaxing a bit, sliding into being disrespectful and downright nasty. You think it shouldn't be a problem because of course they know you love them. But if you're being cruel, using words like "stupid" or "lazy," you'll make an imprint on that person's heart that can't be erased. If you belittle or berate each other you'll develop a thick skin; it will not only protect you from hurtful words but it will keep out the love you're longing for.
3. You stop listening with an open mind. We all want to be right. Every war on the planet has been caused by people thinking they're right and their enemy is wrong. Wanting to be right is an epidemic in this country. Many good relationships fall apart because someone wanted to be right rather than happy. An open mind requires you to stop judging your partner and stop making them wrong. How often have you changed your mind because some one told you you're wrong? That kind of persuasion never works.
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To stop these communication mistakes, check in with yourself every day. It takes constant awareness to keep the feelings of safety and trust you had in the begining alive. The biggest saboteur of a good relationship is the breakdown of communication, when you lose your ability to talk to your partner as a friend. So, don't let it happen to you.