Nothing in this thread so far is jealousy. There's a difference between being a jealous, insecure guy and a guy who just has common sense.
well let's say your girlfriend is texting a lot with a guy from work. This hasn't happened to me, but let's work on the basis it has.
It went from nothing, but they are texting quite a lot and she isn't keen on letting you see the messages.
This is your chick acting suspiciously. Jealousy would be if your chick is texting a guy from work,acting normal, yet you still are worrying what she's texting about. If your chick suddenly is texting some guy, and you see her hiding her phone all of a sudden, its common sense something is amidst.
ok, let me take this one step further...
You then hear she slept overnight at this guy's place as the office went out late and she couldn't get home.
Is that an issue?
Again, this is a chick doing something many would consider inappropriate.
In the morning I call with a girl I've been dating (nothing official but we only sleep with eachother) and we arrange to meet up during the afternoon to go for a walk when I'm back from the gym. I called her when I got back but she wasn't feeling that good anymore and wanted to stay at home. I said sure no problem and went out with some friends instead.
Later that day she texts me what I'm doing and tells me she's at a winebar with another guy who asked her to go out for a drink (a guy she has been trying to make me jealous with before). I replied with ' Haha seriously?' and then stopped replying to her texts. (she said: What? Am I not allowed? followed by random texts telling me she was home and asking me what I'm doing). Eventuelly she called me asking me why I wasn't answering anymore and if I was upset.
This is a chick playing games and being dishonest. Jealousy would be, if you were fucking a chick with no relationship, and you actually were wondering if she were out with another guy or what she talks to other guys about. This is just a game player.