It's basically creating an imaginary friend, except "different" somehow?
Tried to find a decent representative article or video, but didn't really feel comfortable linking to any of them.
The biggest impression I got from looking into the concept was that these people were profoundly lonely.
I thought the husband had an entirely valid request of "Your tulpa can't be in a sexual relationship with someone else"
Obviously I don't know anything about the situation beyond what is in the podcast, but up until that point it seemed like a "my husband won't accept my quirks" type of thing.
After they read his excerpt, I was much more inclined to think she was really the one at fault for their relationship falling apart.
All I can say is I'm glad I'm not having to deal with that situation.