I broke up with my girlfriend because she was taking pictures and flirting with other guys?

Ok I misunderstand what you mean by taking pictures. If you mean sending them to those other guys then you were most probably in the right, unless she was like best friends with these guys, and yes that is possible. I am a girl and I am best friends with a guy, and that's not weird. If she was literally JUST taking pictures yet still "flirting" to other guys then again you were most probably in the right, but it still could have been just for fun, aka "banter". Some people find it easier to text than to talk and that's sometimes a sign of social anxiety and antisocial behaviour. But it happens to the most of us, which is kind of sad. Anyways, you never know it could have just been friendly and the were joking around. The only way you'll actually know is if you saw the messages and I'm presuming you did and you checked for hidden jokes and sarcasm, but sometime they aren't that easy to see and they're maybe private jokes between the two. So yea.. I hope this helps in some way! :)