Immediately, the thought of it becomes unbearable. It constricts the brain, depriving it of oxygenated happiness until slowly your joyful loving memories begin to blackout in your head. That's when it begins. Like the lights dimming in a theater, once all else fades, a slideshow of what they did, what it must have looked like, begins to play on loop behind your eyes. Every bite of the lower lip, every euphorically strained facial expression, every second of decadent ecstasy.
As other thoughts begin to seep back in and the lights go back up, every scene ignites like gunpowder in the back of your skull. It isn't just sadness anymore, it's pain that burns your mind and radiates through every nerve in your fragile body. The smoke clears and you can think about other things again, but the inferno has left the ashes imprinted on the inside of your eyelids. Every time you close your eyes, you see it all again.
Of course, you didn't actually see any of it. It's all just what your psyche, in the fragile state it's in, imagines it to have been like. You would think that helps, not actually having seen it, but it doesn't. It doesn't give you the certainty of fact, the assurance of exactly how it happened as observed. No, now since you're left to recreate the scenes in your mind, the ash impressions on your eyelids are exaggerated. You assume that every single thing that could have happened to make it worse, did. You fill in spaces unnecessarily, adding dreadful detail that may or may not be correct (though you are convinced it is) everywhere you can.
It's only a matter of time before you start examining and over-examining every single detail of both your relationship and what happened.
Were they willing to do this to you the whole time you were dating? Remember that day early on? When you drove through the October mist, windows down and music blaring as you both screamed the lyrics to your favorite songs through the cool damp night?
That first time you said those dreaded three words once the beat faded and you pulled up to the house just giggling and smiling at each other, then you kissed under the stars? Did that mean anything to them at all? Did they really love you back then? Do they love you now? They keep saying they do.
How could they love you? How could anyone? You're unlovable. You're not good enough, you will never be enough for them. That's why they did what they did. At least, that's what you keep telling yourself. It's what keeps ringing through your ears in the recreated tone of their voice. Even as the months pass or sometimes even years, the words will still reverberate off the prison cell bars of your skull.
You'll only be convinced of it more and more as time passes and you find yourself still single. Your confidence after what happened will be nothing more than the gum stuck to the bottom of their shoe, constantly getting crushed again and again by their full weight. You'll become convinced that nobody will ever love you again, that you have nothing to love, that nobody would ever conceivably want to be in a relationship with you ever again.
And then someone does. They're sweet, they're caring, and most importantly, they make you happy. Things progress just as they normally would, only with one difference. You still bare the scar of being cheated on. You'll find yourself, early on at least, questioning if this new person in your life really means what they say and if you can trust them. You'll start drawing comparisons between their words and actions and that of your former partner. You'll find it hard to trust again. You'll find it hard to love again.
Now, everything I've written so far may not be certain. Of course, this sort of thing varies from person to person and no one account of being cheated on is true to the experiences of everyone that has ever been cheated on. This next part though, this is the only part that I can say with near absolute certainty, will happen eventually for anyone who has gone through having a partner cheat on them:
This new person will prove your fears to be wrong. They will love you, and you will allow yourself to love them. They will be trustworthy, they will be respectful, and the last thing that they would ever want to do is hurt you. Their affection will cleanse the ash marks on the back of your eyelids and mute the hissing voice in your head. In due time, they will make the pain of your last heartbreak disappear, until one day it all just becomes like a distant nightmare to you. One that they have woken you up from.