Thanks everybody. Advice is appreciated.
My H and I talked for about 3 hours last night about this, and we agreed that going NC with 'Jane' is best. My only issue is getting her to take it like an adult. When she feels wronged, she tends to lash out. She is a coworker, and she tends to gossip. She's kept quiet about everything so far because she and I are still friends, but I fear what she'll tell my supervisors and other coworkers, who have no business knowing anything. My H and I have decided to be totally honest with her about why, about how all evidence points to her having an A with 'Ralph', about how she lied to us about it, about how she continually lies to Ralphs Wife, and about how we can't have that in our lives as we try to rebuild. There's a chance she'll take it like an adult and we can go our separate ways amicably, but there is a better chance she'll get angry and go on the offensive.
As for why we have been good friends, there are a lot of reasons. We have fun together, we can communicate and work well together, we enjoy many of the same things, etc. I know I've listed a lot of her bad qualities, that she gets angry, that she lashes out, that she gossips, and that's mainly a way to try and force myself to focus on those, so ending things will be easier. She's not all bad, she'll go through hell and back to help someone she considers a friend, and she'll defend someone no matter the consequences to herself.
One of my biggest reasons for wanting to end it with her is because I believe she is setting me up for betrayal down the line. I do truly think she's having an A with 'Ralph', and I believe she's choosing to side with Ralph and Ralph's Wife by claiming I'm lying and I'm just trying to hurt them. I confronted her and asked her why she thinks I'd risk my H, my house, my entire way of life, over a lie, and she had no answer for me.
Back in November, before D-Day, I had sent her messages asking her how to gracefully end my friendship with Ralph. I stopped seeing Ralph in a sexual way a year and a half before D-Day, and I wanted to stop seeing him in a friendly way as well. I had previously and repeatedly told him that he needed to stop flirting and stop trying to get me alone, but he always kept up with the "I miss you"'s and the "We should catch up" 's, and the surprise drop ins at work. I was sick of it, and sick of him not listening to me when I told him I was done. Anyway, after I asked her advice, Ralph ceased trying to talk to me, and only glares daggers at me when I accidentally run into him. I know 100% that Jane went straight to him and told him that I wanted to never talk to him again. On one hand, I was relieved because it stopped his persistence, but on the other I had stressed that she needed to not say anything until I figured out the best way to handle things.
So in conclusion, I want any advice you guys can give me on how to damage control this as much as possible. I am hoping to be able to end this like adults, where my H and I sit down with her and explain our side of everything, explain why we can't continue to have her in our life, and why we'll be ceasing contact with her. I'm hoping that, if we give her a chance to defend herself against our "accusations" and give us her side, we can end it like adults, so she doesn't feel like we're ganging up on her.