My boyfriend left his Facebook open on my phone and I read a few messages. They were from another girl. I confronted him about the inappropriate message about two weeks ago. And today it happens again same girl. They both say that they are only friends but the messages were very flirty as I understood them. Am I over reacting?

Depends on the contents and how flirtatious those messages are. Sometimes with a guy is in a relationship with someone already and is texting another girl that isn't his girlfriend he may just be ideally flirting with her with no intentions at all, but that being said he could also be doing that for the reason that you are overacting.

Some guys and girls just enjoy flirting for fun that doesn't lead to anything, but it doesn't hurt to be careful? In case it leads to something. Plus I doubt your boyfriend will be stupid enough to have an affair of some sort by using your phone to Facebook and message another girl.

It's really going to depend on what was actually said but at the face of it, I would say there is probably something going on. At the very least, it is clear that he doesn't respect you. You confronted him about it once but here he is doing it again. I'm friends with lots of women on FB but I don't write "flirty" messages back and forth.