I think he would be able to move on if she left him alone. I think his feelings for her are normal, not really romantic, but confusing to him. Try to imagine if you had an ex or someone that a romantic relationship just didn’t work out with, and this person would text you love you and other romantic sentiments even though you were happy with a new man. You would feel confused, like something dragging you back.
In my experience, it’s not a good idea to talk to him about this either because he will insist that he is in control and has no feelings for her. Men don’t see the little games that women play.
I would not say these types of things to a married man, out of respect for his wife. So why is she pushing this boundary? You could say this next time this comes up. Make him question her actions as well without being defensive. It is clearly making him upset and it’s not healthy.