My girlfriend just came home with her hair all a mess & a hickey on her neck. Cheating?

My girlfriend allegedly went out for girls night last night around 5. Was trying to get a hold of her since 7. Her phone died. & she shows up at our place this AM looking like she had a rough night & a hickey on her neck. Safe to say she is cheating?
My girlfriend just came home with her hair all a mess & a hickey on her neck. Cheating?
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