I am not sure what asking him would achieve. He will likely lie, then defensive, then twist it so that you are at fault for snooping. It will not go well.
Hope - He more than likely had someone over. It was more than likely a woman. But it could have been a mate. You don't know. They get real secretive even about the things they don't need to be secretive about.
I found out my H started dating about 7 months after he MO - I ran into them on a date. It was awful. It brought back all the same confusion, pain and anguish of the initial BD. But, after much soul searching (and a less than dignified confrontation) I decided dating was something he needed to do as part of whatever journey he is on. How was he ever going to work out if the grass is greener if he doesn't walk on the grass?
I don't know where the dating led too. I suspect it led to no-where. But either way I left him to it.
He will try on the single suit to see if it fits irrespective of whether you confront him or not. If you push him on it he will just get better at hiding it.
