Thanks for the thoughtful reply!
Yes, we've been doing a great deal of holding each other, falling asleep in each other's arms. At the moment, he's pretty sick (flu), and that's definitely a stressor, and also makes cuddling not so great.
We talked into the night last night, and definitely realized that the flu was part of the trigger for this particular episode of doubt and anxiety. She went out for a drink with a couple, at his suggestion, even though he had to back off (it was to have been the four of us). When she came home all aglow, using phrases like "I have so much room in my heart to love everyone..." It just sent him to that dark place
One thing we've talked about during all of that holding each other time (and at other times too) is setting some boundaries around language. On the one hand, he wishes she would reserve the word "love" for their relationship, and find other words ("care deeply," "great friendship") for the other ones, including the long-distance boyfriend. On the other hand, he recognizes that it's a bit silly to take the role of language police. The feelings don't change based on his need to hear and not hear certain words. That is, if she loves him -- if she's in love with him -- then avoiding the words is just silly. Furthermore, it only reinforces her sense of him as someone with a need to maintain some degree of control over her.
What he really wants, in his heart of hearts, is for her NOT to love him. He wants her to have a friend. He's got compersion around the fact that her days pass more enjoyably with a chat buddy, and he's also got compersion around the sexual component (he's always had that in the swinging, too -- nothing more beautiful than her having a blast in the bedroom). But he's not sure he's built to be a hinge on a V, and he's not convinced that this is going to end anywhere other than there. She assures him that's not what she intends, and he believes that she means it...but after 20 years of marriage, he knows her propensity for taking everything she does "all the way." It's one of her best qualities :-)
Thanks again for your response.