Cheating is the apology that doesn't get to be elegant. Three drafts: short, full, no-excuses. Pick the one that matches what's true.
Name what you did in plain language, without euphemism. Don't ask for forgiveness in the same message, don't promise it will never happen again, and don't sign off with 'I love you.' A real apology for cheating owns the betrayal and then gets out of the way so the other person can decide what comes next. It is not a negotiation.
The first thing most people do when they apologize for cheating is reach for a softer word. “I made a mistake.” “Something happened.” “I messed up.” The softer the word, the smaller you are trying to make it, and the other person can feel that math happening in real time.
A mistake is forgetting their birthday. What you did has a name, and they already know it. Using the plain word, cheated, slept with someone, kissed someone, lied to you for weeks, does two things at once: it tells them you are not going to make them argue you down to the truth, and it takes the work of naming it off their shoulders. That is the first kindness available to you here, and it is the only one that builds anything.
An apology and a request for forgiveness are two different messages, and they should not arrive together. When “I’m sorry” and “please forgive me” show up in the same text, the apology stops being about them and becomes a transaction: I gave you the words, now give me the absolution.
Forgiveness, if it comes, is theirs to offer on their own clock. Your job in this message is the ownership, full stop. If you find yourself adding “please,” “give me a chance,” or “I can’t lose you” to the end, cut it. Those lines move the weight of the moment back onto the person you hurt, and they will notice.
“It will never happen again” feels like the responsible thing to say. In the wreckage of an affair it reads as something closer to manipulation, because it asks the other person to make a decision based on a guarantee you have no standing to give. They have no reason to trust your future right now. You just spent your credibility.
Skip the promise. Let your actions over the next weeks or months be the only argument for it. If you want to gesture at change, name a concrete thing you are actually doing, ending the contact, telling them everything, getting into therapy, not a sweeping vow about who you will be forever.
The hardest part of a real apology is the ending, because everything in you wants to keep going until they say it’s okay. It is not going to be okay inside one text, and trying to get there is how a sincere apology curdles into pressure.
Own it, tell them you understand if they need space, and close. Send it from your own phone, in your own words. The three drafts below are a starting point, the honest one, the short one, the one without excuses. Take the one that sounds like you and say the rest in person, where this conversation actually belongs.