My one and only life

I remember coming home late one night in college, sophomore year. My roommate was enjoying the late night reality classic, Cheaters. We watched it as a joke, laughing at couples screaming at each other over billiard tables, women pulling each others' hair, and interviews with the weeping protagonists explaining how their spouse had promised never to "do this" again after "last time".
"Once a cheater, always a cheater," my roommate stated as we climbed into our respective beds.

For some reason that comment has stuck with me.

I think that the same goes for liars. Have you ever known someone who has had a series of unusual experiences that don't seem to add up? Have their circumstances ever started to make more sense after you catch them in a lie? As a rule, growing up, I would second guess myself rather than someone else. Maybe I was confused, or remembered something wrong, or there was a misunderstanding. Nowadays, I'm a little more jaded. I still give people the benefit of the doubt initially, but when things don't seem to make sense, they're on thin ice. And once I have proof that the person has lied in the past, why should I believe anything else they say that sounds suspicious? Sure, some of it is probably true, but why should I have to play the fool? That's not fair.

I'm not happy about this. Maybe if I were in a more stable phase in my life, with a  long-term job, relationship, and residence, I would gloss over more offenses. It's not fun being suspicious or angry. It degrades relationships. It's stressful and I feel like I always have to justify being so defensive. But what else can I do? Words don't mean much if they've only been empty promises in the past.