Teenage girls have been stopping at "just kissing" for ages. If they can do it, why wouldn't an adult woman with far more self-confidence and personal boundaries be able to do it? She's not a slave to her biological impulses, she can stop wherever the hell she wants to. I used to send my boyfriend home with blackballs all the time when I was 16. He got over it and still came back for more kissy-kissy on the couch.
That being said, I don't disagree with giving a disclaimer when you start kissing that this is as far as you intend to go. I don't like ugly labels like "cocktease" because I think they're shaming, but it's just easier to have that conversation before everyone is all hot and bothered. If they don't want to stop at just kissing, it's only fair to give them an out before it gets awkward.
As for how to have the talk, I would just basically say what you've said here, even print out your post and have him read it. You've explained yourself pretty clearly, outlined your needs and feelings, and indicated what you would like to happen going forward.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."