It's fine to for deployed persons to attend military functions with someone else. If you have an issue with it, discuss it with your spouse. Just because he was at an event with another woman, doesn't mean he behaved inappropriately with her. At this point, no one knows that but the two of them.
EDIT: Yes, he COULD attend a ball without a partner. He apparently chose not to do that. Again, sounds like you need to speak with him about it. Clearly he doesn't have a problem with you knowing about it, or he wouldn't have allowed photos to be taken and posted on social media, where you could see them.