As long as WH is a WH, don't be surprised about him choosing anything and everything above the family. Of course it hurts, but expect it and don't let it weigh you down more than you can help.

Honestly, a WS who picks their family first on ANYTHING probably did so by accident.

Once he's ready to be a FORMER WS it'll be time to talk turkey and establish firm boundaries. For now, your future boundaries are only expressed verbally, whether they're concerning the OW or the IL's. Positive statements are always better than telling what you won't do.

"I am only willing to be part of a M that contains 2 people."
"It is important to me to have a husband that puts his family first."
"The life I am going to lead does not have room in it for [insert any bad behavior - adultery, alcoholism, drama - whatever the case may be]."

Boundaries are not enforced until Plan B and beyond, but repeated verbal expression of them establishes them as familiar concepts.

Thank you, Neak. I appreciate the advice- especially the part about the repeated verbal expression. I will definitely do that. WH is trying, but he has a lifetime of habits to overcome, as do I (I'm a bit of a quicker learner, though).