How did he come to being tasked as a bodyguard....did she ask him ...did she ask you and you ask him ...did he volunteer?
What about the other methods to stay safe...restraining order, home security system...pistol grip shotgun, local law enforcement and the advent of the cellphone( 911 or emergency #'s )
I guess I'm confused as to where the break down in the poly logic is?
Sex is sex ...love is love. They seem to think it will be just sex....which your ok with ...at least in the past. You seem a bit wiser and more realistic as to the possibility of more....which is poly ...right.
You and husband are poly so no conflict there.
The close friend/ sister thing.....it ok if he sticks his fist or dick up her but not develop feelings or have her as additional loving partner? Isn't that against the poly doctrine?
It seem incredible that the two of you would actually talk about the therapeutic nature of this ....he must be a sexual healer too. I hope she been part of these discussions. It's all about the healin:
New meaning to healing hands /fists
I think if you just use the poly logic you should be ok. Look at the fear... address the fear...talk through the fear.