What to do?

guest
Some of you might remember my post from yesterday. 
I found these fuzzy socks behind the couch of the guy I am seeing. They were next to his work jacket. They were not there a few days ago.
I was too scared to confront him till hours later. 
When I asked if they were his 
He paused for a little and made a face like he was thinking. 
Then he said "I don't remember where I got them or who gave them to me but I used them to to clean a part on my truck."
Then he said they were better because of the toe parts. 
How does he not remember who gave them to him and they aren't that dirty. 
I want to text him and say "have you slept with anyone since we started sleeping together". Is that bad to say? I want to know and don't want to wait till later to ask in person.