An issue within a relationship that constitutes one partner breaking up with the other. Note that they do not need to be a "good" reason by society's standards, but are specific and individual to each relationship.
I can't believe he broke up with her because she didn't put out after 10 dates. I guess to him, that was a "deal breaker".
Some aspect of a deal you make with another person (could be anything from a job offer to a relationship) that prevents you from being able to do it.
When you're facing a situation where there are catches to something, the deal breaker is that one catch that you cannot overlook and/or tolerate.
After looking at this job offer, I could tolerate the lousy shifts, poor pay and even the job being not that great. Having to put up with a two hour drive two and from work every day? Sorry but that's the deal breaker.
An insensitive term used by a partner in a relationship to refer to the often materialistic demands expected to be gained from the opposite partner's expense. That is, a "deal breaker" is a goal, requirement, or condition that must be met in order to keep the other person's supposed love for you.
Female partner: If we cannot afford a wedding within the next three months, that's a deal breaker for me.
Male partner: If you cannot be patient, that's a deal breaker for me.