Re STDs. I wouldn't put a whole lot of energy into talking about this. The only way to protect yourself from STDs is to assume he is having unprotected sex and act accordingly. Only in the context of a recommitted monogomous R AFTER you have had STD tests should you consider doing anything different.
People having affairs lie, no matter how much you ask them to tell you the truth. People who had affairs continue to lie, long after steps toward reconciliation are taken. People who had affairs may very well NEVER tell the truth.
What you are looking for is a promise that either he won't cheat or he will be honest with you about what he does if he cheats. Both promises are NOT worth the words with which they are uttered when people are not in a committed monogomous R in which there is love, openness, trust, and reassurance.
Nikki, I don't think that your WAS is the sole exception here. My point is not to make you feel bad. Rather, it is to (1) Encourage you to act like anyone else not in a monogomous committed R needs to do these days: practice safe sex. Don't ask what he has been doing, you can't trust his answers. Simply, practice safe sex, whatever that is for you. And, you should know that condoms do not protect 100% against any STD nor particularly well at all when it comes to herpes. (2) Don't use the STD talk to cover for your real message in MC. Your real message would probably be: "H, it is OK for you to move out as long as you continue to act like my H." But, this won't get you anywhere. H doesn't want to feel M to you. Emotionally, he probably doesn't feel M to you. You have got to accept that your H-W R is gone. If you have one in the future, it will need to be a new R. Of course, I'm sure that you also have a real concern about STDs that needs to be addressed and a desire to set a clear boundary. You can do this without trying to control him right now or putting yourself in a position where you have to "doubt him" to protect yourself in the future. Simply: "H, neither of us knows where this S will go. So, I just want to put a clear boundary in place. Any sexual activity between us will need to be safe sex. This is nonnegotiable."
Of course, if sometime in the future you are fully reconciled and in a committed monogomous R and have both been tested, then perhaps it would make sense to reconsider. But, for now, don't play with your health by making it part of the R dynamic.
Take your spreadsheet in your purse, but don't be too quick to pull it out unless you really need it. Identify the things that need to be addressed and collaborate in MC to find solutions, rather than trying to tell him how things will be.
This, of course, does not mean that you shouldn't be firm about not moving out. I'll tell you, though, I really wish I had been the one to move out. First, I wouldn't have been waiting for XH to "come home" all the time, I definitely would have been in a better frame of mind sooner. Second, I wouldn't have been left with the tons of stuff that still needs to be gone through, sorted, disposed of, etc... Third, when I got D, H and I had equal debt -- my debt was our old shared debt that was in my name, his debt was all new debt that he'd racked up getting his new place and new stuff. But, in the court's eyes, debt is debt, we were similarly positioned. (I still say NOT FAIR, lol.)