Which is why the CIA mode you don't really want to do is probably going to be needed. You should spy as you simply cannot trust his promises. He's proven he's a liar. And you'll be on pins and needles until you know the truth, or as much of it as can be found out. Take an interest in the cell phone bills, the miles on his car, and demand transparency. You can
Read about that in lots of places here. And see the STD test results, don't just take his word for it. It doesn't sound like OW' s first rodeo, so you don't want to be exposed to every disease in town.
I know these are not comforting words, but your health and sanity are at risk right now.