What is the number one deal breaker in a relationship?

Besides cheating, of course, its not being a good communicator. Some women keep all of their feelings inside and never learn to express and show their true feelings. My ex was like that; she could not, or would not, ever communicate well about anything. She was shy to the point of being emotionally crippled. I was so patient through the years, but could never bring her out of that shell. And our marriage ended, in large part, because of it. It was like talking to a stranger in the end; communication is essential in a good marriage.

Definitely clinginess. Nothing worse than a girl texting me all day, everyday. And having her holding onto me all the time.
I like my own private space and a lot of it.

"clinginess"/dependence---for example, a girl calling me more than once a day to find out whats going on or just to talk nothing when I'm at work, or doing other stuff, or the girl not giving me enough space....