1. Saying the other person is "everything" to you. Or any other statement that makes it sound like you'd be nothing without them. The sentiment is sweet. But subconsciously, it can make you less independent, and way too codependent.
2. Constant communication. You don't HAVE to talk on the phone every night to the person you're dating. And you shouldn't expect your husband or wife to respond to every text message immediately. Remember, you both have your own lives.
3. Doing everything together. Again, it's all about having your own life. So doing stuff together is good. But doing too much together can be bad.
4. Being 100% open and honest all the time. The classic example is, "Do I look fat in these jeans?" The correct answer is always, "No way! You're CRAZY." But it applies to other stuff too. Like if someone hits on you at the gym, do you really NEED to them about it? Or will it just make them jealous for no reason?
5. Expressing every single emotion you have about EVERYTHING that happens in your life. Some of it should be self-managed, so don't expect them to fix it. They should definitely be supportive, but don't treat them like they're responsible for your own emotional well-being.