I think that one of the key things in here is about having negotiated consequences as well as negotiated boundaries.
At the time you both agree on the boundaries, then you need to put a "and this is what's going to happen if those are broken" in there, so that consequences are understood. Sometimes those aren't easy to come up with, and they're usually easier if they are logical and concrete (and stuff like this rarely is). Poly is a learning process, because each individual has different requirements and boundaries - looks like you are most definitely learning yours. An example is what happens if a condom breaks when he is with her...
Your husband has broken your trust and your agreements at the very start of this relationship - that's going to make it an uphill battle. I'm really not sure that this is standard NRE stuff - this goes well beyond the cute silliness that is associated with that and into some far more serious territory.
"Listen, or your tongue will make you deaf." - Native American Proverb