A man who has been married for 15 years with two children and a stay at home wife who has a Facebook profile which states he is a single dad who is taking care of his two kids. And when his wife askes about it he exclaims that he's been meaning to change it but has forgotten his password. And when he filled it out the keyboard keys got stuck from dried soda not allowing him to change the typos he hadn't noticed were there.
When your husband doesn't come home after work every night for three years till the early morning is when you know you have a cheating-husband.