Does my girlfriend like a friend too much?

Hi, this is a bit of a long story so ill try and summarise.
Im currently with my girlfriend and we got together last year when we were university flatmates. Another one of our flatmates was an international student butbwe all got on really well as a flat, like a family. However the internatonal student(we'll call him Matt) has gone back to Australia and we've all now started second year. Now heres where im not sure if im overreacting or not. Weve been out clubbing quite a few times, me, my gf and all of our mates, but for quite a few of those nights she's facetimed him whilst were in the club(not in a weird way, but just showshim to everyone and we all say hi). She does say that she misses him and he's like a brother and stuff and I can understand that as we all were so close. But the other night she was msging him whilst we were all goin out again and said "wish you were here x", also she was talking about visiting him over the summer(Going to Australia to see him). Now im not sure if im over reacting but i dont really like this. Should I say something or be worried?