Posting this in the first place should clue you into the fact that you need to work on your game. You are seeking validation from the nebulous concept of manhood, aka PUAs. So, I'd say that probably you didn't handle it correctly.
It's nearly impossible to not be bothered by this kind of shit, but that's the goal. Create a life so great with so many interesting people in it that if your gf is being weird you don't worry about it. Lofty goal, but worthwhile.
Keep in mind that girls are perceptive little vixens. Trying to act natural will come off as acting, better to not have to act.
As an self-glorifying example, the girl I am seeing texts all kinds of guy, hell I don't care, she's hot. I expect that she is flirting with other guys, she better be. When I walk in a room with her every guy is looking at her and I just smile. When I am not with her am I supposed to expect that guys magically stop being interested in her?
Another thing to think about: I'm flirting with other girls as well, it's great fun. Point is, men and women should interact sexually. Yes, at some point you make commitments to someone that you will not develop attachment to anyone else and that you will have sex only with her. But that doesn't mean that either of you should stop flirting and having fun. You should have been doing the same all along. Why weren't you?