You did well to swallow your pride and not turn a dumb situation into a completely fucked up one.
But...
You CANT control how others talk to your girlfriend and if you are gonna be one of *those* guys (one that will pick a fight because some guy is flirting with *your* girlfriend)....you will find yourself alone very quickly.
I've had those boyfriends...and as I explained to them....they can not control how guys talk to me, what is said, what they do....but they can trust me
or not. If its not.....see ya.
Other than that, I wonder....why do you have her password and why were you logged in as her?
Obviously, if there are 60 odd emails, they are more than just acquaintances at work...they are obviously important to each other in some way, shape or form.
Oh...personally, I dont think there is anything wrong with friends saying "love you" to friends...does not matter whether that person has a partner or not.