Dexter, I think you've been quite patient with the guy. I have zero experience in the BDSM lifestyle, but I believe swinging and BDSM parallel one another closely in the need for honesty, trust, and excellent communication. My husband would not take kindly to some guy - whether single or married - texting me with long, wordy conversations that made it obvious the guy would rather that the love of my life wasn't even in the picture. And the sexting/requests for XXX photos...that's just a dealbreaker there. But maybe that's just us.
We have a few good friends with whom we might send an occasional "Hey, how are ya? Say hello to the Mrs/Hubby." kind of text, but we're quite sensitive about whether or not the other people have respect for our relationship. We don't play separately, and we make that clear. We understand that some people have different comfort levels in this respect, but if it becomes obvious that there's a lack of respect for our relationship, or if we sense that they find our relationship inconvenient for their purposes, we tend to back away from those people.
Does this guy know that you're into BDSM? Does he have any experience at all with it? Or did you get an impression from him about what he thinks of it? I have to wonder if he might misunderstand the concepts involved, and may even be purposely provocative, trying to take you down a peg or two. Hopefully I'm not creating a suspicion out of mid-air, but if your gut is telling you this... It's just a thought.
In any case, you might have the Mrs. let him know that, while she appreciates the attention, she's getting a little uncomfortable with the number and kinds of texts she's been getting. It probably should come from her; if it comes from you, it may come across as defensive, and may not stop the behaviour. If it comes from her, it should come across very clearly. Not sure if that helps at all, but best of luck with this.