For some more insight on this would you mind talking about what these fights you had in the past were over? Where she left and stayed with family? And what was the final fight over , where she took of her ring... what was the argument based on that lead up to that?
Is she feeling emotionally or sexually neglected by you? Do you feel you have been giving her adequate attention and making her feel special? Not doing so isn't a justification for falling for another man... obviously its better to end a relationship than cheat... but most women won't fall to another mans 'woo-ing' when they are being 'woo-ed' at home.
What I mean is some guys can take their wife/gf for granted , not tell her how pretty she is, how funny she is, how smart, how charming... and most women need to hear those things, need to feel those things... and if they aren't getting it from the man they love, there are other men out there constantly offering those compliments, offering that attention.
I feel so emotionally connected to my boyfriend, he always makes me feel special and adored and when guys attempt to 'know' me... talk to me, to charm me, it FAILS. I pay no attention to it, I don't need it from them. But there have been times where he is ignoring me in that department where if I were of weaker character I could have succumed to someone elses attention.