NTA

Everyone was lying by omission, and you have no reason to trust any of them. It’s unreasonable to expect you to “move past” something that you just learned about a few minutes ago, while they’ve known for nine or more years.

Your husband deceived you by allowing you to unknowingly become friends with his affair partner.

Spencer deceived you by knowing that he was in a relationship with your husband’s AP, and not informing you or checking in to see how you felt.

Elinor deceived you by saying that she was your friend but again not checking in to see how you felt about her being the AP.

Sure, you could’ve forgiven your husband, but you’re not expected to hang out with his affair partner often or during holidays. You might forgive someone for miss treating you, but that does not mean that you should spend time with them every day. As you stated, it took a while for you to forgive your husband, so you were able to address that betrayal. It may be more complicated when you’re married, Because that’s a different type of forgiveness that’s required and a level of trust that’s lost.

You were never able to acknowledge the trust that you lost in Elinor, nor were you able to address it. It was hidden from you and that was done intentionally by every party involved. At the very least, you should be given time to process all of this, and not have it overwhelm you during the holidays. It is up to you to want to befriend her, but it’s not up to other people to make that decision for you. They were intentionally deceitful so that they can have a relationship with you the way that they wanted without you having a choice.

I definitely do not believe in blaming the AP in the situations, especially if they didn’t know. That doesn’t mean that the AP then gets to to deceive the spouse and intentionally befriend them knowing that the spouse is ill informed.

Whatever decision you make, I hope that you’re comfortable with it. You also deserve to put yourself first and your relationship. Your kids will be okay.