I think she's fooling herself, and she's fooling you by saying she can just be friends with this woman. She's attracted to her, she's developed feelings for her, she's already expressed interest sexually in her, she's exchanged photos with her, and she cannot stop thinking of her after 6 months? One cannot just pull back on an attraction they feel or on feelings they've already developed and just be "friends". Your wife wants to explore further, and is cloaking it under the facade of "just friendship". She's already stepped out of bounds. I don't know what to advise, but if it were me, I'd want to have a serious sit down conversation about what each of us truly wants in the relationship or outside of the relationship and go from there. Therapy may also help you. It sounds like there are definitely other issues going on in the marriage too, so couples therapy may help as well. I'm very sorry you're in this position. I think it's hurtful and I can see you are naturally in pain over it. (((hugs)))