The simple solution is to start calling him a special name (sweetheart, honey, hon, luscious lips, etc.).
I know you can't call him that all the time and I know that isn't what you asked and that's why I said it was the simple solution. :)
You're right that after 16 years of being with one man - and only 7 months with your new man (think how many times you said your ex's name in over 16 years) it is muscle memory. And forming a new habit can take up to 300 consistent repetitions. (So here's another part of the simple solution - say his name over and over even when you're not with him - to retrain your brain.)
Now to the harder part of my advice. I'm concerned that your new boyfriend 'gets so angry' when you slip. You've told him why it happens and you've apologized. Him getting 'so angry' seems inappropriate to me. You're not interested in being with your ex, you're working on it and you don't call him the wrong name every time. And even though you called him the wrong name in front of his parents (the height of embarrassment I'm sure) it's truly not enough to warrant 'getting so angry.'
I suggest you have a conversation with him like this -
I'm so happy to be with you instead of my ex. You're so much better a man than he was because you're (fill in the blank with as many positive traits you can think of). I'm embarrassed when I've called you the wrong name and I'm working hard to not do it again.
I do need to tell you that when I slip and you get so angry it makes me pull away emotionally from you. I'd be grateful if I slip again that instead of getting angry you'd remember I'm doing my best to work on this and not get angry at me. -End of Conversation with your boyfriend-
It'd be happy to practice this conversation with you so you'll feel comfortable saying these words to him. I know you'll both be glad when your ex isn't part of your relationship any more.
And if he can't stop getting angry about this I think you and I would need to have conversation about why you'd want to stay with someone like this.
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