An affair is an affair whether it is physical or emotional. It is completely out of order for him to date and vacation with other women regardless of whether he takes it as far as nudity! That he is vacationing with them, I would say is pretty damning proof on its own. You should expose ANY type of affair, whether it is sexual or not is completely beside the point.

You will need spyware to get really good proof. I discovered 'I love you texts' on his phone that he was deleting immediately after receipt. Of course I didn't care whether they were having sex after seeing proof as damning as that. If you go to the Operation Investigate forum you will get some good tips.

Asking his friends will do no good. Most affairs are kept so secret that only the two people in them know about it. (Anyone with moral courage who knows anything would come and tell you anyway. Some of my ex husbands friends knew about it - I saw their texts to him - but they still deny knowing anything to this day). His friends will also tip him off and prevent any spying efforts.