I'm so sorry that you have need to be here. Everyone here knows the pain you are experiencing right now. We have all felt the dagger that ripped through us after discovering that the partner we chose for life betrayed us. It is pure agony.
Your post really triggered me because my husband said the same thing. He really believed that I would never find out. He told me he always wore a condom but, somehow I managed to get and STD...twice.
The thing is....when he says he is experimenting,exactly what does that mean? Variety? Just sex? It sounds like he is seeing what it feels like to be with a prostitute. He never gave a thought to losing his health, his wife or his children. Now that you know, please don't dismiss it as a "mistake". You need to keep looking because, I agree with the others that this is not something new. It usually takes a little while to get caught because the wife never suspects.
Go get tested pronto and insist that he goes too. He needs to bring the test results to you on the lab's letterhead. Don't believe what he is telling you. You want to but, don't. He is in major damage control mode and will try to convince you that it's not as bad as you are making it out to be. It is bad and will take a very long time to sort it all out so be careful about promising R right now.
Yes, at the very least he belongs on the couch. I totally wish I had made mine leave on dday but, I didn't know what I was doing and hind sight is always 20/20. He is the one who is afraid. Show him just how strong you are. Don't be afraid of causing him to go running to her. She doesn't want him, unless he pays by the hour.
Keep posting honey. This is a rough ride.