Don't feel bad for your thoughts. Of course you want your pain to go away. Of course you do. Is this pg 100% confirmed by a doctor? I just wonder if she is making all this drama up to keep your H? It isn't going to work.
My advice when H talks with you about OW (like him showing you the texts), be vague, don't get into a name-calling game about OW with him. If he told you about the Easter thing and how she was mad he spent Easter with his kids, just say something like "Well, your kids were thrilled to have you there", nothing about OW.
Try to avoid the craziness as much as possible. You are doing great.
