Someone else getting my messages

Green means SMS.

Are y’all in a group chat?

Send a group text message on your iPhone, iPad, or iPod touch - Apple Support

Add and remove people in group text messages - Apple Support

About iMessage and SMS/MMS - Apple Support

Is whoever you’re chatting with possibly sharing an account?

On Mac: Open Messages > open Preferences > select the iMessage tab...

Which telephone numbers and which email addresses are configured? All recognized as yours?

On iPhone or iPad: Settings > Messages > Send & Receive

Which telephone numbers and which email addresses are configured? All recognized as yours?

Best guess is SMS shenanigans. This redirection either intentionally, or due to some configuration error. There are services that offer SMS redirection, for instance. Check both with your cellular provider, and have the other recipient apparently involved check with their provider, as well as checking their device for problems there.

If you're seeing misrouted SMS (green bubbles, not blue bubbles), check with your carrier, too.

Which accounts are configured in iMessage?

Messages > Preferences > iMessages > You can be reached for messages at...

Also see this article: Add or remove your phone number in Messages or FaceTime - Apple Support

I think I had a similar issue as you where I have a friend I’m in a group chat with, and I typed in their name to text them personally, but the text went to the group chat instead. It has only happened to me once so I just figured I made a mistake. I guess my best advice is to delete the group chat (assuming you don’t have important message you need to save from it), and try creating a new text for that friend to test if it works. Click this button to create the new message after deleting the group chat, and when you type in the person’s name, just verify it’s just them and not a group before sending the message.

this is happening to me also, just in the last week or so has happened numerous times. I think I am sending a message to one person and see the chat text above my message, and then it gets sent randomly to someone else. A big problem.

Of those involved in the connection, the carrier should be able to determine whether you've sent one message to one recipient, one message to two recipients, or two messages to two recipients, or if the recipient has forwarded the message, or if there's something else going on. AFAICT, we've run through what can be reasonably gleaned from an iPhone via a forum discussion.

This continues to happen, only on my MacBook air (not on my iPhone). It is happening with messages going as iMessages. These are messages directed to one person, I see the person's account as I am typing the message. When I send it is suddenly opens and appears in a completely different person's messages. This is not user error; I am being obsessively careful as it keeps happening.

I don't understand the question?

It all looks correct

Only my phone # and my apple email account are listed.