First, it's possible he never contacted anyone. A lot of men use escort ads as masturbation material, just as some use dating sites or Craigslist ads that they never intended to reply to. A lot of men even go so far as contacting sex workers and wasting their time just for the sake of jerking off.

Second, if you mention anything about having seen this, it's literally game over. Think about that before you mention anything to him.

Third, if him looking at escort ads or seeing escorts is a problem for you, you have a choice...you can just break up with him and find someone who doesn't do that. But this is why people shouldn't snoop, because you will always find what you're looking for eventually.

I'd also just like to say that terms like "using" contribute to the stigma that sex workers already face. Sex workers get a ton of shit all the time and are already seen as mere Fleshlights with a heartbeat, so even though I know you didn't mean it this way at all, implying even subtly that SWers are to be "used" only bolsters that stigma.

Good luck to you with your situation and I hope you come to a conclusion that makes you happy.