Why did he need to re-add the slut on facebook?

Me and my husband got into the worst argument last year over this woman on facebook he kept flirting back and forth with ("hey sexy", "hey wifey", "hey ms logan" (our last name, btw) and there was this pic where she was sticking her tongue out and he said "put your tongue up unless you are gonna ????" He deleted her, and things got back to semi-normal, then today he added her as a friend again (He made no attemt to conceal that he added her btw). Why would he do that?! Is he trying to start an argument, is he testing my trust? whats the deal...Im just trying to figure out what his thought process was on this one...im confused!