If you have problems loading a keystroke logger or other spy software find a local business that can do it for you. You can remotely follow his texting history, all online chats, sites visited, (eg. is he going to a lawyer) and so on. It is VERY VERY valuable to know these things, I can not stress that enough. Don't feel that you are spying on him, just look at it like you are doing what you need to protect your marriage and family from this other girl. You are also doing this to protect the future of your children should it come down to child support.
In this case it is good for you that he is a JW. The threat of DF'ing is a very strong one. Yes, he may think he can take it for a short while, but maybe he will realize that it could be a long time if you have evidence that what he is doing is planned. Also, as a witness he is still responcible for taking care of his family financially.
I could be way off base here but I am going to guess he does not make too much money. I guess that because as a witness he likey does not have a degree. Another reason I say that is since your children are so young I have to assume that he is not older than 35, if that is the case and he is dumb enough to use an iPod he is sharing with his wife to contact another girl he is probably flipping burgers.