Was your sex life okay before this guy came into her life?
I think this could possibly be a crisis of identity for her and a big dose of NRE over having sex with a man and this man in particular. I don't find her actions intentionally cruel, just confused, self involved and not very caring. If you are not home a lot I would think she is used to doing things on her own and has come to expect that.
If I were in your position I would ask her to slow down on this guy until you get your relationship back on track and sort some of these issues out. Some boundaries wouldn't go a miss about what your expectations are around her seeing him and not paying attention to your needs coming up afterwards. I would also get to know the guy and involve him in these conversations. If he is fucking your wife you are entitled to some face time with him, some recognition of your feelings and input in all of it I reckon.
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