Ahh, sorry, my fault. I was projecting my own search into this to much. Re-reading the OP's post, it does seem she's a heterosexual woman. Funny enough this goes right back to the point of the huge amount of variety that you can get in these relationships.
From that, to keep on the thread of the topic and to further my own understanding, what is the glue that would keep a vee together?
If you were to treat it in my view and promote fidelity (poly-f: thank you for the new term
compared to an open relationship?
Is this possible? Are most/all closed tri's bi or can they be vees?
A tri is appealing to me in that each person is getting the maximum number of "benefits" from the other two, thus leaving to room for discord or complaints. It also allows for the option that if one worked or such the other two would be just as comfortable. For my situation I have a sharply different schedule then my wife. The idea of a tri works perfectly that while I'm gone the two can be comfortable, happy and safe, and while either of them are gone the us two remaining can be comfortable, happy and safe.
Granted, a vee could have the same benefits, provided friendship were an adequate substitute for intimacy in the relationship. Essentially they both have the same application in MY personal lifestyle, I would just be happier with the tri for whatever reason.
Taking the focus off of the OP's husband seems like a good idea. As they're new to this it would be a nice way to work into something real. Allowing them to become comfortable and establish boundaries and what's good/bad. If the third doesn't work out they would have the knowledge and comfort base to find something more personal and dedicated if it was wanted.
When I read the couple-third-couple I must admit I thought of the BDSM scene
It does seem like a possibility though, Not for myself. I enjoy the intimacy and closeness of a relationship to much. It seems that if someone had another couple or partner then it would detract from that special little... thing. I don't even know what to call it but it's certainly there.