disgustedbyme,
First, I'd suggest asking a mod to put the stop sign up. That means that BS's are not allowed to reply, only other WS's such as myself, who have walked in your shoes and faced similar issues and challenges.
I'll just be honest with you, your story doesn't seem honest to me. I don't say that to be mean, rather, as a random stranger on the internet who read your story verbatim, it doesn't smack of truth to me, and if even I can't believe it, then I don't see how your husband is supposed to. I find it difficult to believe that you were texting the wrong guy. But what I believe, and to be honest, what YOU believe, is irrelevant when it comes to your husband and marriage, and I'll tell you why I say that.
You DID text both guys. You did. Now, you may not have intended to message the other guy, that's possible. For the sake of argument, let's say that you really did message the wrong guy and have no idea. The fact is, whether you intended to or not, you DID text both guys. The fact that you couldn't even keep them straight kinda makes it worse honestly. Imagine if your husband was having an affair with a blonde woman, and then you found out he had sex with another woman, and he said, "OMG! I had no idea it was another woman, all I knew was that she was blonde!" Does that seem like a comforting statement to you?
Look, even if all of this is the truth, as I said, it doesn't matter. All WS's have to go through the same process of accepting who we are and what we've done. One of the hardest lessons to learn in this process is the difference between what "is" and what is "perceived", and understanding that what is perceived, is, for all intents and purposes, the truth, at least when it comes to understanding others and the emotions they feel.
Here is what I suggest. Instead of getting defensive and trying to get your husband to believe you that the other guy was an accident, try just owning the fact that neither of these men should have ever been sexting with you, either on purpose or by accident, and that the entirety of that falls on you. Your husband didn't do anything wrong here, he is the victim. The fact that you didn't know who you were texting with makes you less trustworthy, not more. Own that. Take the approach that your husband absolutely does not have a reason to believe you and that you cannot blame him for that.
For what it is worth, and to help explain my point, if some guy at karate practice started to hip thrust at my wife, he wouldn't have to worry about me, as my wife would punch him dead in the face. Not because she respects me, although I'd hope that's part of it. No, she'd do it because she respects herself more than that. I trust my wife because she is authentic, loves and respects herself, and knows who she is. She demands better for herself.
Your job moving forward is to give him reasons to believe in you again, and in order to do that, you'll need to come to terms with how and why you came to the point in your life where it was okay to have an affair. He will believe you when you respect and love yourself, and him, enough to be believable. Until then, his perception is truth.