At this point I am not sure if it would be a deal breaker. I kind of ask myself if I really care. I think those photos don't say much and upon closer review, they aren't even touching. Not to say that doesn't mean anything, but as you say he is in an odd state of mind. He isn't himself. Neither is the girl as she is involved in her own marital issues.
I also don't think he could handle adding another person into the mix. He even told me this. He doesn't want anyone getting in the way of him dealing with his daughter and me. He said this right before I left and I believe him. His sister also confirms this and says he respects me and our marriage too much to be that stupid. But people do stupid things when they are drunk. I am just trying not to be naive. But even my therapist feels cheating is not a factor here. I am not trying to dwell on it anymore.
My gut tells me I am over reacting. I showed the pics to my dad and he said they are not much. He is my dad, he would tell me if he had concern. I have no other proof, so like i said, I am going to let it go for now. There are actually other things breaking the deal more than this. I want to stick it out, but not for the sake of my sanity. I am going to show him I am moving on and see what happens.
You have some great advice. I hope things work out for you.