What would be a relationship deal breaker for you?

I read an interesting agony aunt question, whereby the husband although loving his wife, had decided to leave because she had become overweight.

The agony aunt replied that she understood that this was a dealbreaker for him and that in fact, long story short, he had done the right thing for him. (He just was not attracted to her), but yes he did love her.

Okay, with that thought in mind, I did think most deal breakers were discussed prior to a relationship and most definitely before a marriage. Not during the marriage. Although I understand that some things that can happen during a relationship or marriage can be deal breakers.

So, with that in mind, what would your deal breakers be? What do you think of the guy mentioned situation?