Does not sound good to me tbh. I have been on the receiving end of a serial cheater.
He will come up with a very plausible excuse by 11pm tonight. He will talk his way out of this one.
Use the next few hours to your advantage. If he has been stupid enough to leave the kind of evidence you have already found in your home then there is the possibilty there is more for you to find. You may not feel you can face it just now - but right now is your only chance becfore he gets home to leave no stone unturned and search and search and search for more if you EVER want to get to the bottom of this.
Search everywehere. Pockets of clothing in his wardrobe- even stuff he has not worn in ages, bank accounts, computers , spare mobiles, receipts, look in the car as well.
You are looking for anything that cannot be explained.
He is unlikely to admit to anything and if he does admit to some kind of infidelity you will be drip fed the bare minimum of what he thinks he can get away with telling you. Most men in this situation do the same.
Hold back any further evidence and use it wisely to obtain more info - assuming ofcourse you want to know.
If you choose not to know the facts then expect to find yourself over the coming weeks to find yourself mulling over all kinds of vile and hurtful scenarios. The truth can hurt and be painful but then you can start dealing with that hurt. The unknown just plays on your mind for alot longer and probably causes alot more damage in the long run.
Sorry to be so down on your situation but its similar to situations I have been in. I know the pain. I know the vile thoughts and I know how it eats away unless you face it head on.
Get off the PC now and search everywhere for anything that could point to his infidelity. Mumsnet will still be here later if you need more support. You only have until he comes home tonight to find anything else he may have "hidden" in your home. Now he knows you are onto him, anything that MAY be in your home will be moved pronto by him as he tries to limit any damage already done.
However awful this all is right now - you will one day move on from it one way or another, but burying your head in the sand and hoping it will all be OK, is just delaying the inevitable.