Some context, me and my girlfriend is in a LDR. She has known her girlfriend (let's call her leslie) since high school and was really close with her since high school. (This was way before she knew me). They are now around 10km apart and always travel a long way to see each other for few days.

I have started to worry about my girlfriend and Leslie as they have sleep overs pretty often. This is usually not a problem, but my girlfriend usually doesn't call me for the entire duration of days she's staying in Leslie's place. She still replies to text messages but it takes a few hours to reply, which is very unusual as she always replies text instantly. In addition, they sleep on the same bed and take pictures in bed together when each other's sleeping (I saw it accidentally when she was scrolling through her gallery)? I guess it's a girls thing to take pictures of each other sleeping?

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I need some advice on should I worry about this or should I take some actions on stopping it? It doesn't seem fine to me that I sleep over at a girl's place and share the same bed every now and then.