I'm not sure from your post, but you two sound rather young, and your DH very immature. It doesn't sound like his lies are malicious, but borne out of not being able to stand up and act like a man. I don't mean that as a slam. Men often take longer to mature then women. What I'm saying is that he may "out-grow" this need to cover up issues that he is not fully ready to deal with. How long it will take is hard to say, and whether you can exist through it is also difficult to say.
I'm curious. What were his reasons for keeping this from you? He is acting like a little boy who thinks he was going to be in trouble.
His behavior also speaks to some impulsivity. He agreed to the testing rules, but got horny and broke them.
I believe these are behaviors that can be overcome, but it's going to take some work from him to learn to "man up" so to speak. It would seem some outside help ~ counselor, trusted mentor ~ might be helpful, but again I know the poly issue will confuse most people.