He probably is not cheating outside of sending a dick pic to a complete stranger. Check out r/scams things along this line are an epidemic these days. They fish for enough info to be able to search people on social media so they can threaten to expose it to friends and family. If you post about it on scams they can better explain what is happening.

Your husband should ignore them and apologize one thousand times over for sending a dick pic to some old man in the phillipines