Hi Pink,
Stay calm I know that easy for us to say, but perhaps as it was a suite the boys decided to club together and he just paid for it with his card, and they paid him their share with cash. Most of hotels these days need credit cards to secure rooms and to secure against any damage. Perhaps they wanted a different night out, a bit of pampering and luxury? How many blokes do you know would admit that they wanted that for their night out? If there were no signs of infidelity before then don't look for it now, you know the saying, give a dog a bad name and it will stick.
If he left his statement lying around, he is hardly trying to hide anything, if he is, then he is very stupid. Put it to the back of your mind, and when he comes in later, just ask him what the hotel was like, and that you're thinking of booking a weekend there for the two of you, as a break. If there was anything untoward then he'll squirm and avoid the subject or suggest somewhere else. Take it with a smile and then max his card out for him.
I'm thinking of you and I'm sure everything will be fine.