Its sounds to me you were a shit, you know you were a shit & your wife looked elsewhere for support. This is a *classic* emotional affair scenario, btw.
Did she actually cheat on you? Take it to a physical level? Make plans to leave you for this other guy? Unless she did, I would argue her behaviour may have been simply 'relationship survival'. You still may be able to salvage your marriage with some committed counselling. I would do this asap.
If she did do any of those things, then I guess its a question of where your boundaries lie. And how whatever you did balances those out. Sounds like you've got some hard thinking to do.
Good luck.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh