The fight is over. The apology shouldn't restart it. Three drafts: short, full, no-excuses.
Apologize for your specific part and nothing else. The fastest way to restart a fight is to apologize and relitigate it in the same message, any “I’m sorry, but,” any list of what they did, any “I only said that because.” Own the exact thing that was yours: the raised voice, the cruel line, the walking out. Leave their behavior out of it entirely.
“I’m sorry, but you were also…” is not an apology, it is a ceasefire with terms. The moment “but” shows up, the other person stops hearing the sorry and starts defending against the rest, and you are both back in the fight you were trying to end.
If you need a connector, “and” does the job “but” can’t. “I’m sorry I snapped at you, and I want to talk about the rest when we’re both calmer.” That keeps the apology intact and parks the disagreement for later, instead of smuggling it in under the apology.
Vague apologies, “sorry things got heated,” “sorry we fought”, spread the responsibility evenly across both of you, which is exactly what the person waiting for an apology will notice. Name the specific thing you actually did: you raised your voice, you brought up something from a year ago, you said the cruel line you knew would land, you walked out mid-sentence.
Specificity is what makes an apology believable. “I’m sorry I called you that, it was a cheap shot and I knew it when I said it” tells them you have actually looked at your own behavior. Naming the exact move is the proof that you mean it.
The strongest pull right after a fight is to get your version on the record, to explain why you reacted, what they did first, how it actually went. Every sentence of that undoes the apology. You cannot say sorry and build your case in the same breath; the case is what tells them the sorry was conditional.
There may be a real conversation to have about what they did, and you are allowed to want it. It just doesn’t belong in the apology. Repair first, fully, with nothing attached. The disagreement will still be there tomorrow if it’s real, and it’ll be a lot easier to talk about from a calm place than a defended one.
“Sorry I got loud” addresses the noise. Often the thing that actually hurt was underneath the noise, the contempt, the thing you said that you can’t unsay, the way you made them feel small. If you only apologize for the volume, they are left holding the part that really stung.
Aim the apology at the harm. “I’m sorry, not just for yelling, but for the thing I said about you. That wasn’t fair and it wasn’t true.” That is the apology that ends a fight instead of pausing it. The three drafts below stay clean by design: ownership, no relitigating, no scorekeeping. Pick the one that sounds like you.