Women continue to post Ls online — "Boyfriend has called me his ex's name 3 times in the last 6 weeks"

I started dating this guy in June. We're both in our early 30s. I knew he had ended a 3 year relationship in the summer of 2022. That was the only long term relationship he's had in his adult life, and he's done some casual dating.

Our communication, goals, and values all align really well and things are good, in ways I didn't know relationships could be. He's met my family, we've said I love you (it's early but I truly feel this way), I'm invited on his family's holiday trip and my ticket is booked (by them), etc. I've had some bad dating experiences in the past so I'm pretty jaded and keep watching for the bottom to fall out and it just doesn't. He's progressively becoming a better boyfriend over time instead of worse (which is new for me--I always thought it could only go the opposite way lol).

The issue? He has now called me his ex girlfriend's name 3 times in the last six weeks. And I'm really starting to lose it.

1st time--I had COVID in early August and he took care of me. We went to get grocery pick up order, and while he was getting the order, the attendant asked what the name was, he told her "[Ex's first name] [My last name]." He caught it immediately and apologized to me.

2nd time--He was meeting my family, and we were out on a little sailboat just him and I, and he called me her name. I literally almost jumped overboard.

3rd time--This past weekend. He called me her name in front of one of my best friends, on a weekend out of state trip, while getting ready to go hiking.

I'm trying to figure out the psychology behind this. I'm not a jealous person, but due to my own past traumas, this sets me off like a bomb. He's terrible with names and words (Example: He called my friend by the wrong name after staying with her for 2 days), but I feel like my name should be one he can recall. Additionally, the ex and I do not have phonetically similar names. Her name ends with a different sound, and we begin with different letters as well.

When I've heard him do this, my dark side spins and says "either he's A. Cheating on you with her. or B. Isn't serious about you, because no man would risk throwing away a relationship with a woman he's serious about, by repeatedly calling her by the name of an ex girlfriend he's been broken up with for a year."

Any thoughts? Has anyone experienced this? What do I do?

EDIT: Putting in an edit one commenter mentioned was important: He and the ex still talk. They broke up allegedly on friendly terms (which I want to say is great, but honestly i've seen more people stay unwittingly connected or attached to an ex when things amicable and they immediately transitioned to friends then when there was a clean break), are "friends" and have a shared business venture which is the cause of their texting about at minimum every few weeks. My rational brain says he's probably not cheating on me, but somehow knowing they still text even about non emotional things makes me go to this dark place even easier when he calls me her name.

All this mixed with a nice dose of ostensibly asking for advice while shooting down anything that doesn't validate her paranoia:

What is his response the other two times?

If he's super apologetic, he might just genuinely be bad at names.

He is apologetic, but my brain is like "how apologetic can you be if you keep doing it?"

He seems to feel bad, and apologizes or tries to offer other comfort measures (ie, hug me, kiss, rub my leg) while apologizing, but at that point im so upset its not something i want. If I continue to full court press him about it, or bring it up later, he gets irritated. Ie "yes, i am over her. no, i do not want to get back together with her. I enjoy being with you. Me calling you her name because Im terrible at names doesn't disprove that." [-16]