Why is my girlfriend acting distant?

So I have been seeing my girlfriend for 4 years now and we have been living together for the last 6 months. Everything has been good and it is a normal healthy relationship with the odd ups and downs like everyone.

However she goes back to her home country which is Portugal for a few weeks every summer. In the past I noticed that she became less conversational via texts and video calls as she is spending time with her family and friends. But this time she went without a return ticket as she wants to spend a bit longer this summer. I told her before she left that I don't want her to be a stranger like she has in the past when she went away.

Straight away almost back to her usual antics. I text and she responds but it's usually very short and dry. She leaves me on read A LOT too and it's only when I initiate a video call that she will talk properly. Here's the other problem... After 4 years together I have still yet to meet her family as she says they can be a bit funny when it comes to meeting boyfriends. I haven't gotten mad at her for doing this again but I'm starting to get very upset and concerned. Is she slowly sliding me away?

Why is my girlfriend acting distant?
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