None of your behavior or that you were friends with this guy was inappropriate in the least. Texting, messaging or even phone calls with friends is just that, friends. Whether male or female if that's all it was nothing you said implies any inappropriate behavior at all.

The point of contention is not in either of your behaviors but how the gf views female friends and unfortunately this is not an uncommon thing. In a lot of cases (and btw this is not just with females either) the SO for whatever reason finds that their mate having opposite sex friends is a threat. It matters very little how you act or what you've done in those cases as this is entirely based on the suspicious nature of the gf or bf.

We can go into all kinds of detail as to whether his gf is jealous, controlling or any number of other discussions but it matters very little. Likely she's said something and he's being respectful and choosing to do what he feels is best at the moment for his relationship that matters most, his SO.

Nothing wrong in that but it would be a lot nicer of him to be honest about it and tell you that's the case instead of simply cutting off most communication if not all.