It's judgmental, but kind of understandable. The knee-jerk reaction to infidelity , most of the time, is to tell the person who got jilted to GTFO. After all, once a cheater always a cheater , right? Well, that's not always true. There are many reasons why someone might cheat on their partner , just like there are many reasons why the person who was cheated on might choose to stay in the relationship. "Just because your partner had an affair doesn't mean that you stop loving them," says Carolynn Aristone , LCSW, a sex therapist who specializes in affair recovery. "You've been loving them right up to the moment that you find out about their affair, so what happens then?"