A guy answered my girlfriends phone?

I called my girl and a guy answered the phone, she told me she was sick from drinking the night before but when I called later I'm the day to check up on her she said she was out with friends, later on she said she was sorry and that her phone was in the car and that the guy who answered it always does that. Not sure if I'm being paranoid or if something else is going on.
A guy answered my girlfriends phone?
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