Like: I hope you don't mind me chiming in here.

I have nothing to say that will justify what he's done. Trust is precious and if you can't completely trust someone, you can't trust them at all. On the otherhand, the worst thing that one spouse can do to another in a situation like this is to place the offending spouse in a "fishbowl" inspecting their every movement (please research the psychological concept of "projective identification").

I like what teigyr says and I think counseling is best.

I also encourage you to evaluate your emotions on this; many in this situation would feel "hurt", but "furious" is a much stronger emotion that indicates to me that counseling and reconciliation may be beneficial.

If you both want to work this out, please don't assume that the issues are "one way" in the relationship; if you both don't want to work this out, then counseling isn't going to work.

I wish you the best in sorting this out.