Booo, I am so sorry. There is no pain quite like this. Breathe, and take care of yourself physically. This is taking a huge toll on your body, and it will need extra care to carry you through. And know that you WILL get through, although you can't see that right now.
You need to decide nothing at this point. And he gets no decision-making power on your behalf, unless you choose that. I strongly suggest doing some reading. Shirley Glass' book, Not Just Friends, is a good one.
I agree that an MD check is important, and I also suggest setting aside some funds just for you, just in case. Again, you need decide NOTHING now.
I can't even get into the links between addiction, lying, and infidelity because it's still a rough subject for me - just know that his actions do not reflect upon you. Again, I am so sorry. You are not alone.