Should I have dumped her for texting men friends? She swore it was innocent banter.?

The long and short of it is I dumped my girlfriend for texting with other men. She once told me that the same guys would make a move on her when we split previously so that was my cause for concern. It hurts like mad without her but I did it for my own sanity. Also her phone was "always" on silent. Reason for suspicion. Opinions please. Insecurity or good old fashioned gut instinct?