Is it reasonable not to know if two people are a couple?

I've seen a fellow female student around a few guys each in the past, until she ended up with one of them solely. But beforehand it looked like she was together with each of them one after the other. Like, one was standing close to her almost kissing her, one had his arm around her while talking to the others, and one had even kissed her.

Is it reasonable not to know if two people are a couple?
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