I just wanted to say yeah your a decent guy, and I'm soo sorry. The post suggesting being tested for std's is right on you need to do that right away. It seems to me there is more going on with your wife than simple depression, I would insist on a full psych evaluation, some of her behavior suggests perhaps something like bi-polar disorder. If that were the case then it would shed a whole new light on what was happening with her.
It might be wise to take a close look at your finances, and make sure nothing is going on there, and you also might want to legally have your house in order so to speak. It's awlful to have to think that way but you have children to think about and want to be able to continue providing and caring for them to the best or your ability.
As far as your future with your wife, you have to be able to forgive her and let it go. If you can't both of you will be miserable, because you would always be suspicous of her everytime she walked out the door. If you can't let it go and it would always be on the back of your mind then it might be time to start thinking of parting ways, I hope for your sake and your kids it can all work out and you find peace with whats going on with your wife. If you need any more big sister advice or to just vent we'll be here.