Plus use this analogy:

WAS has a new love interest, exciting person, emotional connection, physical connection, it's great, it's new, it's exciting (I've said exciting already).

WAS has a great spouse who has spent alot of time working on personal development and really is starting to shine.

So they have a "new toy" which is exciting to play with.
And they're discovering their "old toy" is fun to play with too.

When a person has the comfort of being able to make a choice and isn't forced to make a choice immediately, what would motivate the WAS to make a choice at all? When they have a choice between an exciting new lover and a great spouse and no one is making them choose, don't they have the best of both worlds? New & exciting and safe & secure. If both the "new" and "old" toy enable this environment for the WAS and no one wants to rock the boat, what would ever motivate the WAS to make a decision? If there is no fear of loss, the WAS can technically enjoy both.

Sure you can tell the WAS that you won't be in an open relationship but don't they already have the idea in their head that the LBS made a lot of changes to get them back, to impress them, to make them see that the LBS has great value and should be considered?

In this situation, the WAS is with the "new" toy and that is currently their first choice. The WAS also has the "old" toy, that is their second choice, their fallback, their safety net just in case the first option doesn't work out. When we enable this behavior by saying that it's ok that we're 2nd choice don't we communicate lower value indirectly that way?

When we remove that 2nd choice,
fear, jealousy & fear of loss motivates the WAS to make a choice or if we look at this from the LBS perspective, we remove the choice that the WAS had, we remove ourselves from the options list and we show them that it's our choice to make and if we do this by dating, don't we communicate indirectly that they no longer have higher value.

Yes I know I'm totally over thinking all of this but I think alot of this has to be close to be accurate.